Diocletian
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/* Illness and abdication */ Ooh! We've an article for that now.
{{Infobox Roman emperor
|name=Diocletian
| title =[[Roman emperor|Emperor]] of the [[Roman Empire]]
| full name =Gaius Aurelius Valerius Diocletianus<ref>Barnes, ''New Empire'', p. 4. For full imperial titulature, see: Barnes, ''New Empire'', pp. 17–29.</ref>
| image =[[Image:DSC04500i Istanbul - Museo archeol. - Diocleziano (284-205 d.C.) - Foto G. Dall'Orto 28-5-2006.jpg|200px]]
| caption =Diocletian
| reign =[[November 20]] [[284]] – [[April 1]] [[286]] (alone)<br>[[April 1]] [[286]] – [[May 1]] [[305]] (as [[Augustus (title)#In the Divided Roman Empire|Augustus]] of the East, with [[Maximian]] as Augustus of the West)<ref>Barnes, ''New Empire'', p. 4.</ref>
| predecessor =[[Numerian]]
| successor =[[Constantius Chlorus]] and [[Galerius]]
| spouse =[[Prisca (empress)|Prisca]]
| issue =Valeria
| dynasty =
| father =
| mother =
| date of birth =''ca''. [[December 22]] [[244]]<ref name="BIRTH">Barnes, ''New Empire'', pp. 30, 46; Bowman, "Diocletian", p. 68.</ref>
| place of birth =[[Duklja (town)|Dioclea]], near [[Solin, Croatia|Salonae]]<ref>Barnes, ''New Empire'', p. 31; Bowman, "Diocletian", p. 68; Williams, ''Diocletian'', pp. 237–38.</ref>
| date of death =[[December 3]] [[311]]<ref name="DEATH">Barnes, "Lactantius and Constantine", pp. 32–35; Barnes, ''New Empire'', pp. 31–32.</ref>
| place of death =[[Diocletian's Palace|Spalatum (now Split, Croatia)]]
| place of burial =
|}}
'''Gaius Aurelius Valerius Diocletianus''' (''ca''. [[December 22]] [[244]]<ref name="BIRTH"/> – [[December 3]] [[311]]<ref name="DEATH"/>), born Diocles ([[Greek language|Greek]]: Διοκλής) and known as '''Diocletian''' ({{IPAEng|ˌdаɪəˈkliːʃən}}), was [[Roman Emperor]] from [[November 20]] [[284]] to [[May 1]] [[305]]. Born to a [[Dalmatia]]n family of low status, he rose through the ranks of the military to become cavalry commander to the emperor [[Carus]]. After the deaths of Carus and his son [[Numerian]] on campaign in Persia, Diocletian was acclaimed emperor by the army. A brief confrontation with Carus' other surviving son [[Carinus]] at the [[Battle of the Margus]] removed the only other claimant to the title. Diocletian appointed fellow-officer [[Maximian]] his [[Augustus (honorific)|Augustus]], his senior co-emperor, in 285. He delegated further on [[March 1]] [[293]], appointing [[Galerius]] and [[Constantius Chlorus|Constantius]] as [[Caesar (title)|Caesars]], junior co-emperors. Under this "[[Tetrarchy]]", or "rule of four", each emperor would rule over a quarter-division of the empire. In campaigns against [[Sarmatians|Sarmatian]] and [[Danube|Danubian]] tribes (285–90), the [[Alamanni]] (288), and usurpers in [[Roman Egypt|Egypt]] (297–98), Diocletian secured the empire's borders and purged it of threats to his power. In 299, Diocletian led negotiations with [[Sassanid Persia]], the empire's traditional enemy, and achieved a lasting and favorable peace.
Diocletian separated and enlarged the empire's civil and military services and re-organized the empire's provincial divisions, establishing the largest and most [[Bureaucracy|bureaucratic]] government in the history of the Empire. New power centers were established in [[Nicomedia]], [[Mediolanum]], [[Antioch]], and [[Trier]]. These cities were far removed from the traditional capitol at Rome, but were close to the military concerns of the empire. Developing on third-century trends towards absolutism, Diocletian styled himself an autocrat, and divided himself from the empire's masses via imposing forms of court ceremonial and architecture. Bureaucratic and military growth, constant campaigning, and construction projects increased the state's expenditures, and necessitated a comprehensive tax reform. From at least 297 on, imperial taxation was standardized, made more equitable, and levied at generally higher rates.
Not all Diocletian's plans were successful; the ''[[Edict on Maximum Prices]]'' (301), Diocletian's attempt to curb [[inflation]] via price controls, was unsuccessful, counterproductive, and quickly ignored. Although effective while he ruled, Diocletian's Tetrarchic system collapsed after his abdication under the competing dynastic claims of [[Maxentius]] and [[Constantine I|Constantine]], sons of Maximian and Constantius respectively. The [[Diocletianic Persecution]], the empire's last systematic persecution of [[Christianity]], failed to significantly weaken the Church, and by 324, the empire would be ruled by the Christian emperor Constantine. In spite of his failures, Diocletian's reforms fundamentally changed the structure of Roman imperial government and helped stabilize the empire economically and militarily, enabling an empire that had seemed near the brink of collapse in Diocletian's youth to remain essentially intact for another hundred years. Weakened by illness, Diocletian left the imperial office on [[May 1]] [[305]], and became the first Roman emperor to voluntarily abdicate the position. He lived out his retirement in [[Diocletian's Palace|a palace]] on the Dalmatian coast, tending his vegetable gardens.
==Early life==
Diocletian was probably born near [[Salona]] in [[Dalmatia]] ([[Solin, Croatia|Solin]] in modern [[Croatia]]), some time around 244.<ref name="BIRTH"/> His parents named him Diocles, or possibly Diocles Valerius.<ref>Aurelius Victor 39.1; Potter, ''The Roman Empire at Bay'', p. 648.</ref> The modern historian [[Timothy Barnes]] takes [[December 22]] as his birthdate, but other historians are not so certain.<ref>Barnes, ''New Empire'', p. 30; Williams, ''Diocletian'', pp. 237–38.</ref> Diocles' parents were of low status, and writers critical of him claimed that his father was a [[scribe]] or a [[freedman]] of the senator Anullinus, or even that Diocles was a freedman himself. The first forty years of his life are mostly obscure.<ref>Barnes, ''Constantine and Eusebius'', p. 4; Bowman, "Diocletian", p. 68; Potter, ''The Roman Empire at Bay'', p. 280; Williams, ''Diocletian'', pp. 22–23.</ref> The [[Byzantine Empire|Byzantine]] chronicler [[Joannes Zonaras]] states that he was ''[[Dux]] [[Moesia]]e'',<ref>Zonaras, 12.31; Southern, ''Severus to Constantine'', p. 331; Williams, ''Diocletian'', p. 26.</ref> a commander of forces on the lower [[Danube]].<ref>Mathisen, "Diocletian"; Williams, ''Diocletian'', p. 26.</ref> The unreliable ''[[Augustan History|Historia Augusta]]'' states that he served in Gaul, where he received an omen of his future rule, but this statement is not corroborated by other sources.<ref>''SHA'', ''Vita Carini'' 14–15; Williams, ''Diocletian'', p. 26.</ref> In 282, the legions of the upper Danube in [[Raetia]] and [[Noricum]] proclaimed the [[praetorian prefect]] M. Aurelius [[Carus]] as emperor, beginning a rebellion against what had been the apparently secure government of the emperor [[Probus]].<ref>Barnes, ''Constantine and Eusebius'', p. 4; Odahl, ''Constantine and the Christian Empire'', p. 39; Southern, ''Severus to Constantine'', p. 132; Williams, ''Diocletian'', p. 32.</ref> Probus' army, stationed in [[Sirmium]] ([[Sremska Mitrovica]], [[Serbia]]), decided against fighting Carus, and assassinated Probus instead.<ref>Barnes, ''Constantine and Eusebius'', p. 4; Odahl, ''Constantine and the Christian Empire'', p. 39; Southern, ''Severus to Constantine'', p. 132.</ref> Diocles soon gained Carus' trust, for Carus declared him commander of the ''Protectores Domestici'', the cavalry arm of the imperial bodyguard.<ref>Barnes, ''Constantine and Eusebius'', p. 4; Barnes, ''New Empire'', p. 31; Bowman, "Diocletian", p. 68; Mathisen, "Diocletian"; Williams, ''Diocletian'', p. 33.</ref>
Carus, already sixty, wished to establish a dynasty;<ref>Odahl, ''Constantine and the Christian Empire'', p. 39; Southern, ''Severus to Constantine'', p. 132; Williams, ''Diocletian'', p. 32.</ref> he immediately elevated his sons [[Carinus]] and [[Numerian]] to the rank of Caesar.<ref>Barnes, ''Constantine and Eusebius'', p. 4; Odahl, ''Constantine and the Christian Empire'', p. 39; Williams, ''Diocletian'', p. 32.</ref> In 283, Carus raised Carinus to the title Augustus,<ref>Leadbetter, "Carus"; Leadbetter, "Carinus"; Southern, ''Severus to Constantine'', p. 132.</ref> left him in charge of the care of the West, and moved with Numerian, Diocles, and the praetorian prefect [[Aper - L. Flavius Aper|Aper]] to the East, against the [[Sassanid Empire]]. The Sassanids had been embroiled in a succession dispute since the death of [[Shapur]], and were in no position to oppose Carus' advance.<ref>Leadbetter, "Carus"; Odahl, ''Constantine and the Christian Empire'', p. 39.</ref> According to Zonaras, [[Eutropius]], and [[Festus (historian)|Festus]], Carus won a major victory against the Persians, taking [[Seleucia]] and the Sassanid capital of [[Ctesiphon]] (near modern [[Al-Mada'in]], [[Iraq]]), cities on opposite banks of the [[Tigris]].<ref>Zonaras, 12.30; Eutropius, 9.14.1; Festus, 24; Barnes, ''Constantine and Eusebius'', 4; Leadbetter, "Carus"; Odahl, ''Constantine and the Christian Empire'', p. 39; Potter, ''The Roman Empire at Bay'', p. 279; Williams, ''Diocletian'', p. 33.</ref> In celebration, Carus and his sons took the [[Victory title#Roman victory titles|title]] ''Persici maximi''.<ref>Barnes, ''Constantine and Eusebius'', p. 4; Leadbetter, "Carus."</ref> Carus died in July or early August,<ref>Leadbetter, "Carus."</ref> reportedly struck by lightning.<ref>Barnes, ''Constantine and Eusebius'', p. 4; Leadbetter, "Carus"; Odahl, ''Constantine and the Christian Empire'', p. 39; Southern, ''Severus to Constantine'', p. 133; Williams, ''Diocletian'', pp. 33–34.</ref>
==Rise to power==
===Death of Numerian===
[[Image:The Roman Empire ca 400 AD.png|thumb|right|Map of the Roman Empire ''ca''. 400]]
Carus' death left his unpopular sons Numerian and Carinus as the new Augusti. Carinus quickly made his way to Rome from Gaul, and arrived by January 284; Numerian lingered in the East.<ref name="BNSCE4">Barnes, ''Constantine and Eusebius'', p. 4.</ref> The Roman retreat from Persia was orderly and unopposed, for the Persian King, [[Bahram II]], was still struggling to establish his authority.<ref name="SSC133">Southern, ''Severus to Constantine'', p. 133.</ref> By March 284 Numerian had only reached Emesa ([[Homs]]) in [[Syria]]; by November, only Asia Minor.<ref>Barnes, ''Constantine and Eusebius'', p. 4; Leadbetter, "Numerianus."</ref> In Emesa he was apparently still alive and in good health, as he issued the only extant [[rescript]] in his name there.<ref>''[[Codex Justinianus]]'' 5.52.2; Leadbetter, "Numerianus"; Potter, ''The Roman Empire at Bay'', p. 279. Coins are issued in his name in [[Cyzicus]] at some time before the end of 284, but it is impossible to know whether he was still in the public eye by that point (''Roman Imperial Coinage'' 5.2 Numerian no. 462; Potter, ''The Roman Empire at Bay'', pp. 279–80).</ref> After Emesa, Numerian's staff, including the prefect Aper, reported that Numerian suffered from an inflammation of the eyes, and had to travel in a closed coach.<ref>Leadbetter, "Numerianus."</ref> When the army reached [[Bithynia]],<ref name="BNSCE4"/> some of Numerian's soldiers smelled an odor reminiscent of a decaying corpse emanating from the coach.<ref name="SSC133"/> They opened its curtains. Inside, they found Numerian, dead.<ref>Barnes, ''Constantine and Eusebius'', p. 4; Leadbetter, "Numerianus"; Odahl, ''Constantine and the Christian Empire'', p. 39; Williams, ''Diocletian'', p. 35.</ref>
Aper officially broke the news in [[Nicomedia]] ([[İzmit]]) in November.<ref name="P280">Potter, ''The Roman Empire at Bay'', p. 280.</ref> Numerianus' generals and tribunes called a council for the succession, and chose Diocles as emperor,<ref>Barnes, ''Constantine and Eusebius'', p. 4; Bowman, "Diocletian", p. 68; Williams, ''Diocletian'', p. 35–36.</ref> in spite of Aper's attempts to garner support.<ref name="P280">Potter, ''The Roman Empire at Bay'', p. 280.</ref> On [[November 20]] [[284]], the army of the east gathered on a hill three miles {{km to mi|5|km|abbr=yes|precision=1|wiki=yes}} outside Nicomedia. The army unanimously saluted their new Augustus, and Diocles accepted the purple imperial vestments. He raised his sword to the light of the sun, and swore an oath declaiming responsibility for Numerian's death. He asserted that Aper had killed Numerian and concealed it.<ref>Barnes, ''Constantine and Eusebius'', pp. 4–5; Odahl, ''Constantine and the Christian Empire'', pp. 39–40; Williams, ''Diocletian'', pp. 36–37.</ref> In full view of the army, Diocles drew his blade and killed Aper.<ref>Barnes, ''Constantine and Eusebius'', pp. 4–5; Leadbetter, "Numerian"; Odahl, ''Constantine and the Christian Empire'', pp. 39–40; Williams, ''Diocletian'', p. 37.</ref> Soon after Aper's death, Diocles changed his name to the more Latinate "Diocletianus",<ref>Corcoran, "Before Constantine", p. 39.</ref> fully Gaius Aurelius Valerius Diocletianus.<ref>Barnes, ''New Empire'', p. 31; Bowman, "Diocletian", pp. 68–69; Potter, ''The Roman Empire at Bay'', p. 280; Southern, ''Severus to Constantine'', p. 134; Williams, ''Diocletian'', p. 37.</ref>
===Conflict with Carinus===
[[Image:Montemartini - Carino 1030439.JPG|thumb|right|Head of [[Carinus]] at the [[Capitoline Museums#Centrale Montemartini|Centrale Montemartini]]]]
After his accession, Diocletian and Lucius Caesonius Bassus<ref>Fully, L. Caesonius Ovinius Manlius Rufinianus Bassus.</ref> were named as consuls.<ref>Barnes, ''Constantine and Eusebius'', p. 5; Bowman, "Diocletian", p. 69; Potter, ''The Roman Empire at Bay'', p. 280; Southern, ''Severus to Constantine'', p. 134.</ref> They assumed the ''[[fasces]]'' in place of Carinus and Numerianus. Bassus was a member of a [[Campania]]n [[Roman Senate|senatorial]] family, a former consul and a proconsul of Africa. He had been chosen by Probus for signal distinction.<ref name="BNSCE5">Barnes, ''Constantine and Eusebius'', p. 5.</ref> He was a man skilled in areas of government where Diocletian, presumably, had no experience.<ref name="P280">Potter, ''The Roman Empire at Bay'', p. 280.</ref> Diocletian's elevation of Bassus as consul symbolized his rejection of Carinus' government in Rome, his refusal to accept second-tier status to any other emperor,<ref name="BNSCE5">Barnes, ''Constantine and Eusebius'', p. 5.</ref> and his willingness to continue the long-standing collaboration between the empire's senatorial and military aristocracies.<ref name="P280">Potter, ''The Roman Empire at Bay'', p. 280.</ref> It also tied his success to that of the Senate, whose support he would need in an advance on Rome.<ref name="BNSCE5">Barnes, ''Constantine and Eusebius'', p. 5.</ref>
Diocletian was not the only challenger to Carinus' rule; the usurper [[Sabinus Iulianus|M. Aurelius Julianus]], Carinus' ''corrector Venetiae'', controlled northern [[Italy]] and [[Pannonia]].<ref>Barnes, ''Constantine and Eusebius'', p. 5; Bowman, "Diocletian", p. 69; Leadbetter, "Carinus"; Southern, ''Severus to Constantine'', pp. 134–35; Williams, ''Diocletian'', p. 38. See also Banchich.</ref> Julianus took power following Diocletian's accession. He minted coins from the mint at Siscia ([[Sisak]], Croatia) declaring himself as emperor and promising freedom. It was all good press for Diocletian, and aided in his portrayal of Carinus as a cruel and oppressive tyrant.<ref>Southern, ''Severus to Constantine'', pp. 134–5; Williams, ''Diocletian'', p. 38.</ref> Julianus' forces were weak, however, and were handily dispersed when Carinus' armies moved from Britain to northern Italy. With the East under control, Diocletian was clearly a greater threat.<ref>Barnes, ''Constantine and Eusebius'', p. 5; Bowman, "Diocletian", p. 69; Leadbetter, "Carinus."</ref> Over the winter of 284–5, Diocletian advanced west across the [[Balkans]]. In the spring, some time before the end of May,<ref>Bowman, "Diocletian", p. 69; Potter, ''The Roman Empire at Bay'', p. 280.</ref> his armies met Carinus' across the river Margus ([[Great Morava]]) in [[Moesia]]. In modern accounts, the site has been located between the Mons Aureus (Seone, west of [[Smederevo]]) and [[Viminacium]],<ref name="BNSCE5">Barnes, ''Constantine and Eusebius'', p. 5.</ref> near modern [[Belgrade]], Serbia.<ref>Barnes, ''Constantine and Eusebius'', p. 5; Odahl, ''Constantine and the Christian Empire'', p. 40; Southern, ''Severus to Constantine'', p. 135.</ref>
Despite having the stronger army, Carinus held the weaker position. His rule was unpopular; it was subsequently alleged that Carinus had mistreated the Senate and seduced the wives of his officers.<ref>Barnes, ''Constantine and Eusebius'', p. 5; Williams, ''Diocletian'', p. 37–38.</ref> It is possible that [[Constantius Chlorus|Flavius Constantius]], the governor of Dalmatia and Diocletian's associate in the household guard, had already defected to Diocletian in the early spring.<ref>Potter, ''The Roman Empire at Bay'', p. 280; Williams, ''Diocletian'', p. 37.</ref> When the [[Battle of the Margus]] began, Carinus' prefect Aristobulus also defected.<ref>Potter, ''The Roman Empire at Bay'', p. 280.</ref> In the course of the battle, Carinus was killed by his own men. Following Diocletian's victory, both the western and the eastern armies acclaimed him emperor.<ref>Barnes, ''Constantine and Eusebius'', p. 5; Bowman, "Diocletian", p. 69; Odahl, ''Constantine and the Christian Empire'', p. 40; Williams, ''Diocletian'', p. 38.</ref> Diocletian exacted an oath of allegiance from the defeated army and departed for Italy.<ref>Southern, ''Severus to Constantine'', p. 135; Williams, ''Diocletian'', p. 38.</ref>
==Early rule==
Diocletian may have become involved in battles against the [[Quadi]] and [[Marcomanni]] immediately after the Battle of the Margus. He eventually made his way to northern Italy and made an imperial government, but it is not known whether Diocletian visited the city of Rome at this time.<ref>Barnes, ''Constantine and Eusebius'', p. 5; Bowman, "Diocletian", p. 69.</ref> There is a contemporary issue of coins suggestive of an imperial ''[[adventus (ceremony)|adventus]]'' (arrival) for the city,<ref>''Roman Imperial Coinage'' 5.2.241 no. 203–04; Barnes, ''Constantine and Eusebius'', pp. 5, 287; Barnes, ''New Empire'', p. 50.</ref> but some modern historians state that Diocletian avoided the city, and that he did so on principle; the city and its Senate were no longer politically relevant to the affairs of the empire, and needed to be taught as much. Diocletian dated his reign from his elevation by the army, not the date of his ratification by the Senate.<ref>Williams, ''Diocletian'', p. 41.</ref> If Diocletian ever did enter Rome, he did not stay long;<ref>Southern, ''Severus to Constantine'', pp. 135, 331.</ref> he is attested back in the Balkans by [[November 2]] [[285]], on campaign against the [[Sarmatians]].<ref>Potter, ''The Roman Empire at Bay'', p. 281.</ref>
Diocletian replaced the [[Praefectus urbis|prefect]] of Rome with his consular colleague Bassus. Most officials who had served under Carinus, however, retained their offices under Diocletian.<ref>Barnes, ''Constantine and Eusebius'', pp. 5–6; Bowman, "Diocletian", p. 69; Barnes, ''New Empire'', p. 113; Williams, ''Diocletian'', pp. 41–42.</ref> In an act the epitomator [[Aurelius Victor]] denotes as unusual act of ''clementia'',<ref>Aurelius Victor, 39.15, qtd. in Leadbetter, "Carinus."</ref> Diocletian did not kill or depose Carinus' traitorous praetorian prefect and consul Ti. Claudius Aurelius Aristobulus, but confirmed him in both roles,<ref>Barnes, "Two Senators," p. 46; Barnes, ''Constantine and Eusebius'', pp. 5–6; Leadbetter, "Carinus"; Southern, ''Severus to Constantine'', p. 135; Williams, ''Diocletian'', p. 41</ref> and later gave him the proconsulate of Africa and the rank of urban prefect.<ref>Leadbetter, "Carinus."</ref> The other figures who retained their offices might have also betrayed Carinus.<ref>Barnes, "Two Senators," p. 46; Barnes, ''Constantine and Eusebius'', pp. 5–6; Leadbetter, "Carinus."</ref>
===Maximian made co-emperor===
[[Image:Maximian.gif|right|thumb|Maximian was by all accounts a loyal man, in spite of his military and moral inadequacies. His consistent loyalty proved an important component of the Tetrarchy's early successes.<ref>Corcoran, "Before Constantine", p. 40.</ref>]]
Recent history had demonstrated that sole rulership was dangerous to the stability of the empire. The assassinations of [[Aurelian]] (r. 270–275) and Probus testified to that truth.<ref name="P280">Potter, ''The Roman Empire at Bay'', p. 280.</ref> Conflict boiled in every province of the empire, from Gaul to Syria, from Egypt to the lower Danube. It was too much for a single person to control, and Diocletian needed a lieutenant.<ref>Barnes, ''Constantine and Eusebius'', p. 6; Southern, ''Severus to Constantine'', p. 136.</ref> At some time in 285 at [[Mediolanum]] ([[Milan]], Italy),<ref>Barnes and Bowman suggest a date of [[July 21]] (''Constantine and Eusebius'', p. 6; Barnes, ''New Empire'', p. 4; Bowman, "Diocletian", p. 69); Potter suggests a date of [[July 25]] (''The Roman Empire at Bay'', pp. 280–81).</ref> Diocletian raised his fellow-officer [[Maximian]] to the office of [[Caesar (title)|Caesar]], making him co-emperor.<ref>Barnes, ''Constantine and Eusebius'', p. 6; Barnes, ''New Empire'', p. 4; Bowman, "Diocletian", p. 69; Bleckmann; Corcoran, "Before Constantine", p. 40; Potter, ''The Roman Empire at Bay'', pp. 280–81; Williams, ''Diocletian'', pp. 43–45.</ref>
The concept of dual rulership was nothing new to the Roman Empire. [[Augustus]], the first emperor (r. 27 BC–AD 14), had shared power with his colleagues, and more formal offices of co-emperor had existed from [[Marcus Aurelius]] (r. 161–180) on.<ref>Corcoran, "Before Constantine", p. 40. See also: Williams, ''Diocletian'', pp. 48–49.</ref> Most recently, the emperor Carus and his sons had ruled together, albeit unsuccessfully. Diocletian was in a less comfortable position than most of his predecessors, as he had a daughter, Valeria, but no sons. His co-ruler had to be from outside his family. He could not, therefore, be easily trusted.<ref>Potter, ''The Roman Empire at Bay'', p. 280; Southern, ''Severus to Constantine'', p. 136; Williams, ''Diocletian'', p. 43.</ref> Some historians state that Diocletian, like some emperors before him, adopted Maximian as his ''filius Augusti'', his "Augustan son", upon his appointment to the throne.<ref>Bowman, "Diocletian", p. 69; Odahl, ''Constantine and the Christian Empire'', pp. 42–43; Southern, ''Severus to Constantine'', p. 136; Williams, ''Diocletian'', p. 45.</ref> This argument has not been universally accepted.<ref>Bowman, "Diocletian", p. 69; Southern, ''Severus to Constantine'', p. 136.</ref>
The relationship between Diocletian and Maximian was quickly couched in religious terms. Circa 287 Diocletian assumed the title ''Iovius'', and Maximian assumed the title ''Herculius''.<ref>Bowman, "Diocletian", pp. 70–71; Corcoran, "Before Constantine", p. 40; Liebeschuetz, ''Continuity and Change'', pp. 235–52, 240–43; Odahl, ''Constantine and the Christian Empire'', pp. 43–44; Williams, ''Diocletian'', pp. 58–59.</ref> The titles were probably meant to convey certain characteristics of their associated leaders; Diocletian, in [[Jupiter (mythology)|Jovian]] style, would take on the dominating roles of planning and commanding; Maximian, in [[Hercules|Herculian]] mode, would act as Jupiter's [[hero]]ic subordinate.<ref>Barnes, ''Constantine and Eusebius'', pp. 11–12; Bowman, "Diocletian", pp. 70–71; Corcoran, "Before Constantine", p. 40; Odahl, ''Constantine and the Christian Empire'', p. 43; Southern, ''Severus to Constantine'', pp. 136–7; Williams, ''Diocletian'', p. 58.</ref> For all their religious connotations, the emperors were not "gods" in the tradition of the [[Imperial cult (ancient Rome)|Imperial cult]]—although they may have been hailed as such in Imperial panegyrics. Instead, they were seen as the gods' representatives, effecting their will on earth.<ref>Barnes, ''Constantine and Eusebius'', p. 11.</ref> The shift to divine sanctification from military acclamation took the power to appoint emperors away from the army. Divine legitimization was what separated Diocletian and Maximian from potential rivals, more than mere military power or dynastic claims.<ref>Williams, ''Diocletian'', pp. 58–59.</ref> After his acclamation, Maximian was dispatched to fight the rebel [[Bagaudae]] in Gaul. Diocletian returned to the East.<ref>Barnes, ''Constantine and Eusebius'', p. 6; Southern, ''Severus to Constantine'', p. 137.</ref>
===Conflict with Sarmatia and Persia===
Diocletian progressed slowly. By [[November 2]], he had only reached Citivas Iovia (Botivo, near [[Ptuj]], [[Slovenia]]).<ref>''Codex Justinianus'' 4.48.5; ''Fragmenta Vaticana'' 297; Barnes, ''Constantine and Eusebius'', p. 6; Barnes, ''New Empire'', p. 50; Potter, ''The Roman Empire at Bay'', p. 281.</ref> In the Balkans during the autumn of 285, he encountered a tribe of [[Sarmatians]] who demanded assistance from the emperor. The Sarmatians requested that Diocletian either help them recover their lost lands or grant them pasturage rights within the empire. Diocletian refused and fought a battle with them, but was unable to secure a complete victory. The nomadic pressures of the [[European Plain]] remained, and could not be solved by a single war; soon the Sarmatians would have to be fought again.<ref>Southern, ''Severus to Constantine'', p. 143; Williams, ''Diocletian'', p. 52.</ref> He wintered in [[Nicomedia]].<ref>He is placed there by a rescript of [[March 3]] [[286]]. ''Fragmenta Vaticana'' 275; Barnes, ''Constantine and Eusebius'', p. 6; Potter, ''The Roman Empire at Bay'', pp. 281, 649.</ref> There may have been a revolt in the eastern provinces at this time, because Diocletian is brought settlers from [[Asia (Roman province)|Asia]] to populate emptied farmlands in [[Thrace]].<ref>''Panegyrici Latini'' 8(5)21.1; Barnes, ''Constantine and Eusebius'', p. 6.</ref> He visited [[Iudaea Province|Judea]] the following spring.<ref>He is attested there in a rescript of [[May 31]] [[287]]. ''Codex Justinianus'' 4.10.3; 1.51.1; 5.17.3; Barnes, ''Constantine and Eusebius'', p. 6; Barnes, ''New Empire'', pp. 50–51; Potter, ''The Roman Empire at Bay'', pp. 281, 649.</ref> Presumably, he returned to spend the following winter in Nicomedia. Diocletian's stay in the East saw diplomatic success in the conflict with Persia: in 287, Bahram II granted him precious gifts, declared open friendship with the empire, and invited Diocletian to visit him.<ref>Barnes, ''Constantine and Eusebius'', p. 6; Millar, ''Roman Near East'', p. 177.</ref> Roman sources insist that the act was entirely voluntary.<ref>Southern, ''Severus to Constantine'', p. 242.</ref>
Around the same time, perhaps in 287,<ref>Barnes, ''New Empire'', p. 51; Bowman, "Diocletian", p. 73.</ref> Persia relinquished claims on [[Armenia]] and recognized Roman authority over territory to the west and south of the Tigris. The western portion of Armenia was incorporated into the Roman empire and made a province. [[Tiridates III of Armenia|Tiridates III]], [[Arsacid Dynasty of Armenia|Arsacid]] claimant to the Armenian throne and Roman client, had been disinherited and forced to take refuge in the Roman empire after the Persian conquest of 252/3. In 287, he returned to lay claim to the eastern half of his ancestral domain. He encountered no opposition.<ref>Barnes, ''Constantine and Eusebius'', p. 6; ; Bowman, "Diocletian", p. 73; Potter, ''The Roman Empire at Bay'', pp. 292, 651; Southern, ''Severus to Constantine'', p. 143; Williams, ''Diocletian'', p. 52.</ref> Bahram II's gifts were widely recognized as symbolic of a victory in the ongoing [[Roman-Persian Wars|conflict with Persia]]; Diocletian was hailed as the "founder of eternal peace". The events might have represented a formal end to Carus' eastern campaign, which probably ended without an acknowledged peace.<ref>Southern, ''Severus to Constantine'', pp. 242, 360–61.</ref> At the conclusion of discussions with the Persians, Diocletian re-organized the Mesopotamian frontier and fortified the city of [[Circesium]] (Buseire, Syria) the [[Euphrates]].<ref>Bowman, "Diocletian", p. 73; Millar, ''Roman Near East'', pp. 180–81; Southern, ''Severus to Constantine'', p. 143; Williams, ''Diocletian'', p. 52.</ref>
===Maximian made Augustus===
Maximian's campaigns were not proceeding as smoothly. The Bagaudae had been easily suppressed, but [[Carausius]], the man he had put in charge of operations against [[Saxons|Saxon]] and [[Franks|Frankish]] [[Piracy|pirates]] on the [[Saxon Shore]], had begun keeping the goods seized from the pirates for himself. Maximian issued a death-warrant for his larcenous subordinate. Carausius fled the Continent, proclaimed himself Augustus, and spurred Britain and northwestern Gaul into open revolt against Maximian and Diocletian.<ref>Barnes, ''Constantine and Eusebius'', pp. 6–7; Bowman, "Diocletian", pp. 70–71; Potter, ''The Roman Empire at Bay'', pp. 283–84; Southern, ''Severus to Constantine'', pp. 137–41; Williams, ''Diocletian'', pp. 45–47.</ref> Spurred by the crisis, on [[April 1]] [[286]],<ref>Barnes, ''Constantine and Eusebius'', pp. 6–7; Bowman, "Diocletian", p. 69; Potter, ''The Roman Empire at Bay'', p. 282; Southern, ''Severus to Constantine'', pp. 141–42; Williams, ''Diocletian'', pp. 47–48. The chronology of Maximian's appointment as Augustus is somewhat uncertain (Corcoran, "Before Constantine", p. 40; Southern, ''Severus to Constantine'', p. 142): it is sometimes suggested that Maximian was appointed Augustus from the start (Potter, ''The Roman Empire at Bay'', p. 281; Southern, ''Severus to Constantine'', p. 142; following ''De Caesaribus'' 39.17). Some sources date the assumption of the title to [[March 1]] [[286]], following ''BGU'' 4.1090.34 (Bowman, "Diocletian", p. 69).</ref> Maximian took up the title of [[Augustus (honorific)|Augustus]].<ref>Barnes, ''Constantine and Eusebius'', p. 7; Bleckmann; Corcoran, "Before Constantine", p. 40; Potter, ''The Roman Empire at Bay'', p. 282; Southern, ''Severus to Constantine'', pp. 141–42; Williams, ''Diocletian'', p. 48.</ref> Maximian's appointment is unusual in that it was impossible for Diocletian to have been present to witness the event. It has even been suggested that Maximian usurped the title, and was only later recognized by Diocletian in hopes of avoiding civil war.<ref>Potter, ''The Roman Empire at Bay'', p. 649.</ref> Although this suggestion is unpopular, it is clear that Diocletian meant for Maximian to act with a certain amount of independence from Diocletian.<ref>Potter, ''The Roman Empire at Bay'', p. 282; Williams, ''Diocletian'', p. 49.</ref>
[[Image:Antoninianus Carausius leg4-RIC 0069v.jpg|thumb|left|Carausius, rebel emperor of [[Roman Britain]]. Most of the evidence for Carausius' reign comes from his coinage, which was of generally fine quality.<ref>Southern, ''Severus to Constantine'', p. 140.</ref>]]
Maximian realized that he could not immediately suppress the rogue commander, and so, for the whole campaigning season of 287, campaigned against tribes beyond the [[Rhine]] instead.<ref>Barnes, ''Constantine and Eusebius'', p. 7; Bowman, "Diocletian", p. 71; Corcoran, "Before Constantine", p. 40.</ref> The following spring, as Maximian prepared a fleet for an expedition against Carausius, Diocletian returned from the East to meet Maximian. The two emperors agreed on a joint campaign against the [[Alamanni]]. Diocletian invaded Germania through Raetia while Maximian progressed from Mainz. Each emperor burned crops and food supplies as he went, destroying the Germans' means of sustenance.<ref>Rees, ''Layers of Loyalty'', 31; Southern, ''Severus to Constantine'', pp. 142–43; Williams, ''Diocletian'', p. 50.</ref> The two men added territory to the empire and allowed Maximian to continue preparations against Carausius without further disturbance.<ref>Barnes, ''Constantine and Eusebius'', p. 7; Corcoran, "Before Constantine", p. 40; Southern, ''Severus to Constantine'', p. 143.</ref> On his return to the East, Diocletian managed what was probably another rapid campaign against the resurgent Sarmatians. No details survive, but surviving inscriptions indicate that Diocletian took the title ''Sarmaticus Maximus'' after 289.<ref>Barnes, ''New Empire'', p. 255; Southern, ''Severus to Constantine'', p. 144.</ref>
In the East, Diocletian engaged in diplomacy with desert tribes in the regions between Rome and Persia. He might have been attempting to persuade them to ally themselves with Rome, thus reviving the old, Rome-friendly, [[Palmyra|Palmyrene]] [[sphere of influence]],<ref name = "ubdeze">Potter, ''The Roman Empire at Bay'', p. 285.</ref> or simply attempting to reduce the frequency of their incursions.<ref>Williams, ''Diocletian'', p. 63.</ref> No details survive for these events.<ref>Southern, ''Severus to Constantine'', p. 144.</ref> Some of the princes of these states were Persian client kings; a disturbing fact in light of increasing tensions with that kingdom.<ref>Williams, ''Diocletian'', p. 78.</ref> In the West, Maximian lost the fleet built in 288 and 289, probably in the early spring of 290. The panegyrist who refers to the loss suggests that its cause was a storm,<ref>''Panegyrici Latini'' 8(5)12.2; Barnes, ''Constantine and Eusebius'', pp. 7, 288; Potter, ''The Roman Empire at Bay'', pp. 284–85, 650; Southern, ''Severus to Constantine'', p. 143; Williams, ''Diocletian'', p. 55.</ref> but this might simply be the panegyrist's attempt to play down the embarrassment of defeat.<ref>Southern, ''Severus to Constantine'', p. 143; Williams, ''Diocletian'', p. 55.</ref> Diocletian broke off his tour of the Eastern provinces soon thereafter. He returned with haste to the West, reaching Emesa by [[May 10]] [[290]],<ref>''Codex Justinianus'' 9.41.9; Barnes, ''New Empire'', p. 51; Potter, ''The Roman Empire at Bay'', pp. 285, 650.</ref> and Sirmium on the Danube by [[July 1]] [[290]].<ref>''Codex Justinianus'' 6.30.6; Barnes, ''New Empire'', p. 52; Potter, ''The Roman Empire at Bay'', pp. 285, 650.</ref>
Diocletian met Maximian in Milan in the winter of 290–1, either in late December 290 or January 291.<ref>Barnes, ''Constantine and Eusebius'', p. 8; Barnes, ''New Empire'', p. 52; Potter, ''The Roman Empire at Bay'', p. 285.</ref> The meeting was undertaken with a sense of solemn pageantry. The emperors spent most of their time in public appearances. It has been surmised that the ceremonies were arranged to demonstrate Diocletian's continuing support for his faltering colleague.<ref name = "ubdeze"/> A deputation from the Roman Senate met with the emperors, renewing that body's infrequent contact with the imperial office.<ref>''Panegyrici Latini'' 11(3)2.4, 8.1, 11.3–4, 12.2; Barnes, ''Constantine and Eusebius'', pp. 8, 288; Potter, ''The Roman Empire at Bay'', pp. 285, 650; Williams, ''Diocletian'', p. 56.</ref> The choice of Milan over Rome further snubbed the capital's pride. The panegyric detailing the events implies that the true center of the empire is not Rome, but where the emperor sits: "...the capital of the Empire appeared to be there, where the two emperors met."<ref>''Panegyrici Latini'' 11(3)12, qtd. in Williams, ''Diocletian'', p. 57.</ref> Decisions on matters of politics and war were most likely made, but they were made in secret.<ref>Barnes, ''Constantine and Eusebius'', p. 8; Potter, ''The Roman Empire at Bay'', pp. 285, 288.</ref> The Augusti would not meet again until 303.<ref name = "ubdeze"/>
==Tetrarchy==
{{main|Tetrarchy}}
===Foundation of the Tetrarchy===
Some time after his return, and before 293, Diocletian transferred command of the war against Carausius from Maximian to Flavius Constantius. Constantius was a former governor of Dalmatia and a man of military experience stretching back to [[Aurelian]]'s campaigns against [[Zenobia]] (272–73). He was Maximian's praetorian prefect in Gaul, and the husband to Maximian's daughter, [[Flavia Maximiana Theodora|Theodora]]. On [[March 1]] [[293]] at Milan, Maximian gave Constantius the office of Caesar.<ref>Barnes, ''Constantine and Eusebius'', pp. 8–9; Barnes, ''New Empire'', pp. 4, 36–37; Potter, ''The Roman Empire at Bay'', p. 288; Southern, ''Severus to Constantine'', p. 146; Williams, ''Diocletian'', pp. 64–65.</ref> In the spring of 293, in either Philippopolis ([[Plovdiv]], [[Bulgaria]]) or Sirmium, Diocletian would do the same [[Galerius]], husband to Diocletian's daughter Valeria, and perhaps Diocletian's praetorian prefect.<ref>The suggested dates for Galerius' appointment are [[March 1]] and [[May 21]]. There is no consensus on which is correct. Barnes, ''Constantine and Eusebius'', pp. 8–9; Barnes, ''New Empire'', pp. 4, 38; Potter, ''The Roman Empire at Bay'', p. 288; Southern, ''Severus to Constantine'', p. 146; Williams, ''Diocletian'', pp. 64–65.</ref> Constantius was assigned Gaul and Britain. Galerius was assigned Syria, Palestine, Egypt, and responsibility for the eastern borderlands.<ref>Barnes, ''Constantine and Eusebius'', pp. 8–9; Williams, ''Diocletian'', p. 67.</ref>
This arrangement is called the Tetrarchy, from a [[Ancient Greek|Greek]] term meaning "rulership by four".<ref>Southern, ''Severus to Constantine'', p. 145.</ref> The Tetrarchic emperors were more or less sovereign in their own lands, and they travelled with their own imperial courts, administrators, secretaries, and armies.<ref>Corcoran, "Before Constantine", pp. 45–46; Williams, ''Diocletian'', p. 67.</ref> They were joined by blood and marriage; Diocletian and Maximian now styled themselves as brothers. The senior co-emperors formally adopted Galerius and Constantius as sons in 293. These relationships implied a line of succession. Galerius and Constantius would become Augusti after Diocletian and Maximian's departure. Maximian's son [[Maxentius]], and Constantius' son [[Constantine I|Constantine]] would then become Caesars. In preparation for their future roles, Constantine and Maxentius were taken to Diocletian's court in Nicomedia.<ref>Barnes, ''Constantine and Eusebius'', pp. 8–9.</ref>
===Conflict in the Balkans and Egypt===
[[Image:Philae, Trajan's Kiosk, Aswan, Egypt, Oct 2004.jpg|thumb|right|A [[Trajan]]ic temple on the island of [[Philae]], the newly established border between the [[Nobatae]] and [[Blemmyes]] and [[Roman Egypt]]<ref>Barnes, ''Constantine and Eusebius'', pp. 17–18.</ref>]]
Diocletian spent the spring of 293 traveling with Galerius from Sirmium to [[Byzantium]] ([[Istanbul]], [[Turkey]]). Diocletian then returned to Sirmium, where he would remain for the following winter and spring. He campaigned against the Sarmatians again in 294, probably in the autumn,<ref name = "pymwoj">Odahl, ''Constantine and the Christian Empire'', p. 59.</ref> and won a victory against them. The defeat kept the Sarmatians from the Danube provinces for a long time. He built forts north of the Danube,<ref>Barnes, ''Constantine and Eusebius'', p. 17; Williams, ''Diocletian'', pp. 76–77.</ref> at [[Aquincum]] ([[Budapest]], [[Hungary]]), Bononia ([[Vidin]], Bulgaria), Ulcisia Vetera, Castra Florentium, Intercisa ([[Dunaújváros]], Hungary), and Onagrinum ([[Begeč]], Serbia). The new forts became part of a new defensive line called the ''Ripa Sarmatica''.<ref>Williams, ''Diocletian'', p. 76.</ref> In 295 and 296 Diocletian campaigned in the region again, and won a victory over the Carpi in the summer of 296.<ref>Barnes, ''Constantine and Eusebius'', p. 17; Odahl, ''Constantine and the Christian Empire'', p. 59; Southern, ''Severus to Constantine'', pp. 149–50.</ref> By the end of his reign, Diocletian had secured the entire length of the Danube, provided it with forts, bridgeheads, highways, and walled towns, and sent fifteen or more legions to patrol the region. The defense came at a heavy cost, but was a significant achievement in an area difficult to defend.<ref>Williams, ''Diocletian'', p. 77.</ref>
Galerius, meanwhile, was engaged in disputes in [[Upper Egypt]]. He would return to Syria in 295 to fight the revanchist Persian Empire.<ref>Barnes, ''Constantine and Eusebius'', p. 17.</ref> Diocletian's attempts to bring the Egyptian tax system in line with imperial standards stirred discontent, and a revolt swept the region after Galerius' departure.<ref>Barnes, ''Constantine and Eusebius'', p. 17. See also Southern, ''Severus to Constantine'', pp. 160, 338.</ref> The usurper [[Domitius Domitianus|L. Domitius Domitianus]] declared himself Augustus in July or August 297. Much of Egypt, including [[Alexandria]], recognized his rule.<ref name="BNSCE17">Barnes, ''Constantine and Eusebius'', 17.</ref> Diocletian moved into Egypt to suppress him, first putting down rebels in the [[Thebaid]] in the autumn of 297,<ref name = "pymwoj"/> then moving on to siege Alexandria. Domitianus died in December 297,<ref>DiMaio, "Domitius".</ref> by which time Diocletian had secured control of the Egyptian countryside. Alexandria, whose defense was organized under Diocletian's former ''[[Corrector#Roman_Antiquity|corrector]]'' [[Achilleus (emperor)|Aurelius Achilleus]], held out until a later date, probably March 298.<ref>Barnes, ''Constantine and Eusebius'', p. 17; DiMaio, "Domitius".</ref>
Bureaucratic affairs were completed during Diocletian's stay:<ref>Barnes, ''Constantine and Eusebius'', pp. 17–18; Southern, ''Severus to Constantine'', p. 150.</ref> a census took place, and Alexandria, in punishment for its rebellion, lost the ability to mint independently.<ref name = "mjhujr">Southern, ''Severus to Constantine'', p. 150.</ref> Diocletian's reforms in the region, combined with those of Septimus Severus, brought Egyptian administrative practices much closer to Roman standards.<ref>Harries, ''Law and Empire'', p. 173.</ref> Diocletian travelled south along the Nile the following summer, where he visited [[Oxyrhynchus]] and [[Elephantine]].<ref name = "mjhujr"/> In Nubia, he made peace with the [[Nobatae]] and [[Blemmyes]] tribes. Under the terms of the peace treaty Rome's borders moved north to [[Philae]] and the two tribes received an annual gold stipend. Diocletian left Africa quickly after the treaty, moving from Upper Egypt in September 298 to Syria in February 299. He met up with Galerius in Mesopotamia.<ref name="BNCE1718">Barnes, ''Constantine and Eusebius'', pp. 17–18.</ref>
===War with Persia===
{{seealso|Roman relations with the Parthians and Sassanids|Roman-Persian Wars}}
====Invasion, counterinvasion====
In 294, [[Narseh]], a son of Shapur who had been passed over for the Sassanid succession, came to power in Persia. Narseh eliminated [[Bahram III]], a young man installed in the wake of Bahram II's death in 293.<ref>Potter, ''The Roman Empire at Bay'', p. 292; Williams, ''Diocletian'', p. 69.</ref> In early 294, Narseh sent Diocletian the customary package of gifts between the empires, and Diocletian responded with an exchange of ambassadors. Within Persia, however, Narseh was destroying every trace of his immediate predecessors from public monuments. He sought to identify himself with the warlike kings [[Ardashir I|Ardashir]] (r. 226–41) and [[Shapur I|Shapur]] (r. 241–72), the same Shapur who had sacked Roman Antioch and skinned the Emperor [[Valerian (emperor)|Valerian]] (r. 253–260) to decorate his war temple. <ref>Williams, ''Diocletian'', p. 69–70.</ref>
Narseh declared war on Rome in 295 or 296. He appears to have first invaded western Armenia, where he seized the lands delivered to Tiridates in the peace of 287.<ref>Ammianus Marcellinus 23.5.11; Barnes, ''Constantine and Eusebius'', p. 17; Bowman, "Diocletian", p. 81; " Potter, ''The Roman Empire at Bay'', p. 292; Southern, ''Severus to Constantine'', p. 149.</ref> Narseh moved south into Roman Mesopotamia in 297, where he inflicted a severe defeat on Galerius in the region between Carrhae ([[Harran]], Turkey) and Callinicum ([[Ar-Raqqah]], Syria)<ref>Eutropius 9.24–25; Barnes, ''Constantine and Eusebius'', p. 17; Bowman, "Diocletian", p. 81; Millar, ''Roman Near East'', pp. 177–78.</ref> (and thus, the historian [[Fergus Millar]] notes, probably somewhere on the [[Balikh river]]).<ref>Millar, ''Roman Near East'', pp. 177–78.</ref> Diocletian may or may not have been present at the battle,<ref>Potter, ''The Roman Empire at Bay'', p. 652.</ref> but he quickly divested himself of all responsibility. In a public ceremony at Antioch, the official version of events was clear: Galerius was responsible for the defeat; Diocletian was not. Diocletian publicly humiliated Galerius, forcing him to walk for a mile at the head of the imperial caravan, still clad in the purple robes of the emperor.<ref>Eutropius 9.24–25; Theophanes, ''anno'' 5793; Barnes, ''Constantine and Eusebius'', p. 17; Bowman, "Diocletian", p. 81; Potter, ''The Roman Empire at Bay'', pp. 292–93.</ref>
[[Image:Arch-of-Galerius-1.jpg|right|thumb|Detail of [[Galerius]] attacking [[Narseh]] on the [[Arch and Tomb of Galerius#Arch_of_Galerius|Arch of Galerius]] at [[Thessaloniki]], [[Greece]], the city where Galerius carried out most of his administrative actions<ref name = "zdbdxf">Southern, ''Severus to Constantine'', p. 151.</ref>]]
Galerius was reinforced, probably in the spring of 298, by a new contingent collected from the empire's Danubian holdings.<ref>Barnes, ''Constantine and Eusebius'', p. 18; Bowman, "Diocletian", p. 81; Millar, ''Roman Near East'', p. 178.</ref> Narseh did not advance from Armenia and Mesopotamia, leaving Galerius to lead the offensive in 298 with an attack on northern Mesopotamia via Armenia.<ref>Millar, ''Roman Near East'', p. 178; Potter, ''Roman Empire at Bay'', p. 293. [[Faustus of Byzantium]]'s history refers to a battle that took place after Galerius set up base at [[Satala]] (Sadak, Turkey) in [[Armenia Minor]], when Narseh advanced from his base at Oskha to attack him (Bowman, "Diocletian", p. 81). Other modern histories of the period do not note these events.</ref> It is unclear if Diocletian was present to assist the campaign; he might have returned to Egypt or Syria.<ref>Lactantius (''DMP'' 9.6) derides Diocletian for his absence from the front; Southern (''Severus to Constantine'', pp. 151, 335–36), on the basis of a dating of the African campaigns one year earlier than that given by Barnes, places him at Galerius' southern flank.</ref> Narseh retreated to Armenia to fight Galerius' force, to Narseh's disadvantage; the rugged Armenian terrain was favorable to Roman infantry, but unfavorable to Sassanid cavalry. In two battles, Galerius won major victories over Narseh. During the second encounter, Roman forces seized Narseh's camp, his treasury, his harem, and his wife.<ref>Barnes, ''Constantine and Eusebius'', p. 18; Potter, ''The Roman Empire at Bay'', p. 293.</ref> Galerius continued moving down the Tigris, and took the Persian capital at Ctesiphon before returning to Roman territory along the Euphrates.<ref>Barnes, ''Constantine and Eusebius'', p. 18; Millar, ''Roman Near East'', p. 178.</ref>
====Peace negotiations====
Narseh sent an ambassador to Galerius to plead for the return of his wives and children in the course of the war, but Galerius had dismissed him.<ref name="BNSCE18">Barnes, ''Constantine and Eusebius'', p. 18.</ref> Serious peace negotiations began in the spring of 299. Diocletian and Galerius' ''magister memoriae'' (secretary) Sicorius Probus was sent to Narseh to present terms.<ref name="BNSCE18">Barnes, ''Constantine and Eusebius'', p. 18.</ref> The conditions of the peace were heavy;<ref name="P293">Potter, ''The Roman Empire at Bay'', p. 293.</ref> Armenia returned to Roman domination, with the fort of Ziatha as its border; [[Caucasian Iberia]] would pay allegiance to Rome under a Roman appointee; Nisibis, now under Roman rule, would become the sole conduit for trade between Persia and Rome; and Rome would exercise control over the five satrapies between the Tigris and Armenia: [[Ingilene]], Sophanene ([[Sophene]]), Arzanene ([[Aghdznik]]), [[Corduene]] (Carduene), and [[Zabdicene]] (near modern [[Hakkâri]], Turkey). These regions included the passage of the Tigris through the [[Anti-Taurus Mountains|Anti-Taurus]] range; the [[Bitlis]] pass, the quickest southerly route into Persian Armenia; and access to the [[Tur Abdin]] plateau.<ref>Millar, ''Roman Near East'', p. 178–79; Potter, ''Roman Empire at Bay'', p. 293.</ref>
A stretch of land containing the later strategic strongholds of Amida ([[Diyarbakır]], Turkey) and Bezabde came under firm Roman military occupation.<ref name="M178">Millar, ''Roman Near East'', p. 178.</ref> With these territories, Rome would have an advance station north of Ctesiphon, and would be able to slow any future advance of Persian forces through the region.<ref name="P293"/> The Tigris was said to have become the boundary between the two empires, but what this means is unclear, as the satrapies listed all lie on the far side of the river. Millar suggests that the satrapies might have been held under a loose Roman hegemony, without military occupation.<ref name="M178"/> At the conclusion of the peace, Tiridates regained both his throne and the entirety of his ancestral claim.<ref name="BNSCE18"/> Rome secured a wide zone of cultural influence, which led to a wide diffusion of [[Syriac Christianity]] from a center at Nisibis in later decades, and the eventual Christianization of Armenia.<ref name="P293"/>
==Religious persecutions==
{{main|Diocletianic Persecution}}
===Early persecutions===
At the conclusion of the peace, Diocletian and Galerius returned to Syrian Antioch.<ref name = "zdbdxf"/> At some time in 299, the emperors took part in a ceremony of [[sacrifice]] and [[divination]] in an attempt to predict the future. The [[haruspex|haruspices]] were unable to read the entrails of the sacrificed animals, and blamed Christians in the imperial household. The emperors ordered all members of the court to perform a sacrifice to purify the palace. The emperors sent letters to the military command, demanding the entire army perform the required sacrifices or face discharge.<ref>Lactantius, ''DMP'' 10.1–5; Barnes, "Sossianus Hierocles", p. 245; Barnes, ''Constantine and Eusebius'', pp. 18–19; Burgess, "Date of the Persecution", pp. 157–58; Helgeland, "Christians and the Roman Army", p. 159; Liebeschuetz, ''Continuity and Change'', pp. 246–8; Odahl, ''Constantine and the Christian Empire'', p. 65.</ref> Diocletian was conservative in matters of religion, a man faithful to the traditional Roman pantheon and understanding of demands for religious purification,<ref>Barnes, ''Constantine and Eusebius'', p. 20; Corcoran, "Before Constantine", p. 51; Odahl, ''Constantine and the Christian Empire'', pp. 54–56, 62.</ref> but [[Eusebius of Caesarea|Eusebius]], [[Lactantius]] and [[Constantine I|Constantine]] state that it was Galerius, not Diocletian, who was the prime supporter of the purge, and its greatest beneficiary.<ref>Lactantius, ''DMP'' 10.6, 31.1; Eusebius, ''Historia Ecclesiastica'' 8, app. 1, 3; Constantine, ''Oratio ad Coetum Sanctum'' 22; Barnes, ''Constantine and Eusebius'', pp. 19, 294.</ref> Galerius, even more devoted and passionate than Diocletian, saw political advantage in the politics of persecution. He was willing to break with a government policy of inaction on the issue.<ref name="BCE19">Barnes, ''Constantine and Eusebius'', p. 19.</ref>
Antioch was Diocletian's primary residence from 299 to 302.<ref>Barnes, ''New Empire'', p. 49.</ref> He visited Egypt once, over the winter of 301–2, and issued a grain dole in Alexandria.<ref name="BCE19"/> Following some public disputes with [[Manichaeism|Manicheans]], Diocletian ordered that the leading followers of [[Mani (prophet)|Mani]] be burnt alive along with their scriptures. In a [[March 31]] [[302]] rescript from Alexandria, he declared that low-status Manicheans must be executed by the blade, and high-status Manicheans must be sent to work in the quarries of Proconnesus ([[Marmara Island]], Turkey) or the mines of Phaeno in southern [[Palestine]]. All Manichean property was to be seized and deposited in the imperial treasury.<ref>''Inscriptiones Latinae Selectae'' 660; Barnes, ''Constantine and Eusebius'', p. 20.</ref> Diocletian found much to be offended by in Manichean religion: its novelty, its alien origins, the way it corrupted the morals of the Roman race, and its inherent opposition to long-standing religious traditions.<ref>Lactantius, ''DMP'' 33.1; Barnes, ''Constantine and Eusebius'', p. 20; Williams, ''Diocletian'', pp. 83–84.</ref> Manichaeanism was also supported by Persia at the time, compounding religious dissent with international politics.<ref>Williams, ''Diocletian'', pp. 78–79, 83–84.</ref> Excepting Persian support, the reasons why he disliked Manichaenism were equally applicable, if not more so, to Christianity, his next target.<ref>Barnes, ''Constantine and Eusebius'', p. 20.</ref>
[[Image:ChristPeterPaul.jpg|thumb|Catacomb of Saints Marcellinus and Peter on the [[Via Labicana]]. Christ between [[Saint Peter|Peter]] and [[Paul of Tarsus|Paul]]. To the sides are the martyrs Gorgonius, Peter, Marcellinus, [[Tiburtius and Susanna|Tiburtius]]]]
===Great Persecution===
Diocletian returned to Antioch in the autumn of 302. He ordered that the [[deacon]] [[Romanus of Caesarea]] have his tongue removed for defiling the order of the courts and interrupting official sacrifices. Romanus was then sent to prison, where he was executed on [[November 17]] [[303]]. The arrogance of this Christian displeased Diocletian, and he left the city for Nicomedia in the winter, accompanied by Galerius.<ref>Barnes, ''Constantine and Eusebius'', pp. 20–21.</ref> According to Lactantius, Diocletian and Galerius entered into an argument over imperial policy towards Christians while wintering at Nicomedia in 302. Diocletian argued that forbidding Christians from the bureaucracy and military would be sufficient to appease the gods, but Galerius pushed for extermination. The two men sought the advice of the [[oracle]] of [[Apollo]] at [[Didyma]].<ref>Lactantius, ''DMP'' 10.6–11; Barnes, ''Constantine and Eusebius'', p. 21; Odahl, ''Constantine and the Christian Empire'', p. 67.</ref> The oracle responded that "the just on earth"<ref>Eusebius, ''Vita Constantini'' 2.50.</ref> hindered Apollo's ability to provide advice. These "just", Diocletian was informed by members of the court, could only refer to the Christians of the empire. At the behest of his court, Diocletian acceded to demands for universal persecution.<ref>Barnes, ''Constantine and Eusebius'', p. 21; Odahl, ''Constantine and the Christian Empire'', p. 67; Potter, ''The Roman Empire at Bay'', p. 338.</ref>
On [[February 23]] [[303]], Diocletian ordered that the newly built church at Nicomedia be razed. He demanded that its scriptures be burned, and seized its precious stores for the treasury.<ref>Barnes, ''Constantine and Eusebius'', p. 22; Odahl, ''Constantine and the Christian Empire'', pp. 67–69; Potter, ''The Roman Empire at Bay'', p. 337; Southern, ''Severus to Constantine'', p. 168.</ref> The next day, Diocletian's first "Edict against the Christians" was published.<ref>Barnes, ''Constantine and Eusebius'', p. 22; Williams, ''Diocletian'', p. 176.</ref> The edict ordered the destruction of Christian scriptures and places of worship across the Empire, and prohibited Christians from assembling for worship.<ref>Barnes, ''Constantine and Eusebius'', p. 22; Liebeschuetz, ''Continuity and Change'', pp. 249–50.</ref> Before the end of February, a fire destroyed part of the imperial palace.<ref name="B24S168">Barnes, ''Constantine and Eusebius'', p. 24; Southern, ''Severus to Constantine'', p. 168.</ref> Galerius convinced Diocletian that the culprits were Christians, conspirators who had plotted with the [[eunuch]]s of the palace. An investigation was commissioned, but no responsible party was found. Executions followed anyway, and the palace eunuchs Dorotheus and [[Gorgonius]] were executed. One individual, Peter, was stripped, raised high, and scourged. Salt and vinegar were poured in his wounds, and he was [[Boiling to death|slowly boiled]] over an open flame. The executions continued until at least [[April 24]] [[303]], when six individuals, including the [[bishop]] [[Anthimus of Nicomedia|Anthimus]], were [[decapitation|decapitated]].<ref name="BCE24">Barnes, ''Constantine and Eusebius'', p. 24.</ref> A second fire occurred sixteen days after the first. Galerius left the city for Rome, declaring Nicomedia unsafe.<ref name="B24S168"/> Diocletian would soon follow.<ref name="BCE24"/>
Although further persecutionary edicts followed, compelling the arrest of the Christian clergy and universal acts of sacrifice,<ref>Barnes, ''Constantine and Eusebius'', pp. 23–24.</ref> the persecutionary edicts were ultimately unsuccessful; most Christians escaped punishment, and even pagans were generally unsympathetic to the persecution. The [[martyr]]s' sufferings strengthened the resolve of their fellow Christians.<ref>Treadgold, ''Byzantine State and Society'', p. 25.</ref> Constantius and Maximian did not apply the later persecutionary edicts, and left the Christians of the West unharmed.<ref>Southern, ''Severus to Constantine'', p. 168.</ref> Galerius rescinded the edict in 311, announcing that the persecution had failed to bring Christians back to traditional religion.<ref>Barnes, ''Constantine and Eusebius'', p. 39.</ref> Within twenty-five years of the persecution's inauguration, the Christian emperor Constantine would rule the empire alone. He would reverse the consequences of the edicts, and return all confiscated property to Christians.<ref>Barnes, ''Constantine and Eusebius'', pp. 48–49, 208–213.</ref> Under Constantine's rule, Christianity would become the empire's preferred religion.<ref>Barnes, ''Constantine and Eusebius'', pp. 208–213.</ref>
==Later life==
===Illness and abdication===
[[Image:SPLIT-Hebrard overall color restitution.jpg|thumb|[[Diocletian's Palace]] at Salona ([[Split]], [[Croatia]])]]
Diocletian entered the city of Rome in the early winter of 303. On [[November 20]], he celebrated, with Maximian, the twentieth anniversary of his reign (''vicennalia''), the tenth anniversary of the Tetrarchy (''[[decennalia]]''), and a triumph for the war with Persia. Diocletian soon grew impatient with the city. It did not give enough deference to his supreme authority; it expected him to act the part of an aristocratic ruler, not a monarchic one. On [[December 20]] [[303]],<ref name = "tkuqen">Potter, ''The Roman Empire at Bay'', p. 341.</ref> Diocletian cut short his stay in Rome and left for the north. He did not even perform the ceremonies investing him with his ninth consulate; he did them in [[Ravenna]] on [[January 1]] [[304]] instead.<ref>Barnes, ''Constantine and Eusebius'', pp. 24–25.</ref> There are suggestions in the ''[[Panegyrici Latini]]'' and Lactantius' account that Diocletian arranged plans for his and Maximian's future retirement of power in Rome. Maximian, according to these accounts, swore to uphold Diocletian's plan in a ceremony in the [[Temple of Jupiter (Capitoline Hill)|temple of Jupiter]].<ref>''Panegyrici Latini'' 7(6)15.16; Lactantius, ''DMP'' 20.4; Southern, ''Severus to Constantine'', pp. 152, 336.</ref>
From Ravenna, Diocletian left for the Danube. There, possibly in Galerius' company, he took part in a campaign against the Carpi.<ref name = "tkuqen"/> He contracted a minor illness while on campaign, but his condition quickly worsened and he chose to travel in a [[Litter (vehicle)|litter]]. In the late summer he left for Nicomedia. On [[November 20]], he appeared in public to dedicate the opening of the circus beside his palace. He collapsed soon after the ceremonies. Over the winter of 304–5 he kept within his palace at all times. Rumors alleging that Diocletian's death was merely being kept secret until Galerius could come to assume power spread through the city. On [[December 13]], he seemed to have finally died. The city was sent into a mourning from which it was only retrieved by public declarations of his survival. When Diocletian reappeared in public on [[March 1]] [[305]], he was emaciated and barely recognizable.<ref>Barnes, ''Constantine and Eusebius'', p. 25; Southern, ''Severus to Constantine'', p. 152.</ref>
Galerius arrived in the city later in March. According to Lactantius, he came armed with plans to reconstitute the Tetrarchy, force Diocletian to step down, and fill the imperial office with men compliant to his will. Through coercion and threats, he eventually convinced Diocletian to comply with his plan. Lactantius also claims that he had done the same to Maximian at Sirmium.<ref>Lactantius, ''DMP'' 18.1–7; Barnes, ''Constantine and Eusebius'', p. 25; Southern, ''Severus to Constantine'', p. 152.</ref> On [[May 1]] [[305]], Diocletian called an assembly of his generals, traditional companion troops, and representatives from distant legions. They met at the same hill, {{km to mi|5|km|abbr=yes|precision=1|wiki=yes}} out of Nicomedia, where Diocletian had been proclaimed emperor. In front of a statue of Jupiter, his patron deity, Diocletian addressed the crowd. With tears in his eyes, he told them of his weakness, his need for rest, and his will to resign. He declared that he needed to pass the duty of empire on to someone stronger. He thus became the first Roman emperor to voluntarily abdicate his title.<ref>Barnes, ''Constantine and Eusebius'', pp. 25–27; Lenski, "Reign of Constantine," p. 60; Odahl, ''Constantine and the Christian Empire'', pp. 69–72; Potter, ''The Roman Empire at Bay'', pp. 341–42.</ref>
Most in the crowd believed they knew what would follow; Constantine and Maxentius, the only adult sons of a reigning emperor, men who long been preparing to succeed their fathers, would be granted the title of Caesar. Constantine had traveled through Palestine at the right hand of Diocletian, and was present at the palace in Nicomedia in 303 and 305. It is likely that Maxentius received the same treatment.<ref>Barnes, ''Constantine and Eusebius'', pp. 25–26.</ref> In Lactantius' account, when Diocletian announced that he was to resign, the entire crowd turned to face Constantine.<ref>Lactantius, ''DMP'' 19.2–6; Barnes, ''Constantine and Eusebius'', p. 26; Potter, ''The Roman Empire at Bay'', p. 342.</ref> It was not to be: [[Flavius Valerius Severus|Severus]] and [[Maximinus|Maximin]] were declared Caesars. Maximin appeared and took Diocletian's robes. On the same day, Severus received his robes from Maximian in Milan. Constantius succeeded Maximian as Augustus of the West, but Constantine and Maxentius were entirely ignored in the transition of power. This did not bode well for the future security of the Tetrarchic system.<ref>Lenski, "Reign of Constantine," p. 60–61; Odahl, ''Constantine and the Christian Empire'', pp. 72–74; Southern, ''Severus to Constantine'', pp. 152–53.</ref>
===Retirement and death===
Diocletian retired to his homeland, Dalmatia. He moved into the expansive [[Diocletian's Palace|palace]] he had built on the [[Adriatic Sea|Adriatic]] near the administrative center of Salona. Maximian retired to villas in [[Campania]] or [[Lucania]].<ref>Barnes, ''Constantine and Eusebius'', p. 27; Southern, ''Severus to Constantine'', p. 152.</ref> Their homes were distant from political life, but Diocletian and Maximian were close enough to remain in regular contact with each other.<ref>Southern, ''Severus to Constantine'', p. 152.</ref> Galerius assumed the consular ''fasces'' in 308 with Diocletian as his colleague. In the autumn of 308, Galerius again conferred with Diocletian at [[Carnuntum]] ([[Petronell-Carnuntum]], [[Austria]]). Diocletian and Maximian were both present on [[November 11]] [[308]], to see Galerius appoint [[Licinius]] to be Augustus in place of Severus, who had died at the hands of Maxentius. He ordered Maximian, who had attempted to return to power after his retirement, to step down permanently. At Carnuntum people begged Diocletian to return to the throne, to resolve the conflicts that had arisen through Constantine's rise to power and Maxentius' usurpation.<ref>Barnes, ''Constantine and Eusebius'', pp. 31–32; Lenski, p. 65; Odahl, ''Constantine and the Christian Empire'', p. 90.</ref> Diocletian's reply: "If you could show the [[cabbage]] that I planted with my own hands to your emperor, he definitely wouldn’t dare suggest that I replace the peace and happiness of this place with the storms of a never-satisfied greed."<ref>Aurelius Victor, ''Liber de Caesaribus'' 39.6.</ref>
He lived on for three more years, spending his days in his palace gardens. He saw his Tetrarchic system implode, torn by the selfish ambitions of his successors. He heard of Maximian's third claim to the throne, his forced suicide, his ''[[damnatio memoriae]]''. In his own palace, statues and portraits of his former companion emperor were torn down and destroyed. Deep in despair and illness, Diocletian may have committed [[suicide]]. He died on [[December 3]] [[311]].<ref>Barnes, ''Constantine and Eusebius'', p. 41.</ref><ref name="DEATH"/>
==Reforms==
===Tetrarchic and ideological===
[[Image:Diocletian's Palace.png|thumb|Modern view of [[Diocletian's Palace]] near [[Salona]] (in [[Split]], [[Croatia]])]]
Diocletian saw his work as that of a restorer, a figure of authority, whose duty it was to return the empire to peace, and recreate stability and justice where barbarian hordes had destroyed it.<ref>Potter, ''The Roman Empire at Bay'', pp. 294–95.</ref> He arrogated, regimented and centralized political authority on a massive scale. In his policies, he enforced an imperial system of values on a diverse and sometimes unwilling provincial audience.<ref>Potter, ''The Roman Empire at Bay'', p. 298.</ref> In the imperial propaganda from the period, recent history is perverted and minimized in the service of the theme of the Tetrarchs as "restorers". Aurelian's achievements are ignored, the revolt of Carausius is backdated to the reign of Gallienus, and it is implied that the Tetrarchs engineered Aurelian's defeat of the [[Palmyrene Empire|Palmyrenes]]; the period between Gallienus and Diocletian is effectively erased. The history of the empire before the Tetrarchy is portrayed as a time of civil war, savage despotism, and imperial collapse.<ref name = "oqujbw">Potter, ''The Roman Empire at Bay'', pp. 296–98.</ref> In those inscriptions that bear their names, Diocletian and his companions are referred to as "restorers of the whole world",<ref>''Inscriptiones Latinae Selectae'' 617, qtd. in Potter, ''The Roman Empire at Bay'', pp. 296.</ref> men who succeeded in "defeating the nations of the barbarians, and confirming the tranquility of their world".<ref>''Inscriptiones Latinae Selectae'' 641, qtd. in Potter, ''The Roman Empire at Bay'', p. 296.</ref> Diocletian was written up as the "founder of eternal peace".<ref>''Inscriptiones Latinae Selectae'' 618, qtd. in Potter, ''The Roman Empire at Bay'', pp. 296. See also Millar, ''Roman Near East'', p. 182, on Tetrarchic triumphalism in the Near East.</ref> The theme of restoration was conjoined to an emphasis on the uniqueness and accomplishments of the Tetrarchs themselves.<ref name = "oqujbw"/>
The cities where emperors lived frequently in this period—Milan, [[Trier]], [[Arles]], Sirmium, [[Serdica]], [[Thessaloniki]], Nicomedia, and [[Antioch]]—were treated as alternate imperial seats, to the exclusion of Rome and its senatorial elite.<ref>Corcoran, "Before Constantine", pp. 44–45.</ref> A new style of ceremony was developed, emphasizing the distinction of the emperor from all other persons. The quasi-republican ideals of Augustus' ''[[primus inter pares]]'' were abandoned for all but the Tetrarchs themselves. Diocletian took to wearing a gold crown and jewels, and forbade the use of [[Tyrian purple|purple cloth]] to all but the emperors.<ref>Corcoran, "Before Constantine", p. 43; Potter, ''The Roman Empire at Bay'', p. 290.</ref> His subjects were required to prostrate themselves in his presence (''adoratio''); the most fortunate were allowed the privilege of kissing the hem of his robe (''[[proskynesis]]'', προσκύνησις).<ref>Corcoran, "Before Constantine", p. 43; Liebeschuetz, ''Continuity and Change'', pp. 235–52, 240–43.</ref> Circuses and basilicas were designed with to keep the face of the emperor perpetually in view, and always in a seat of authority. The emperor became a figure of transcendent authority, a man beyond the grip of the masses.<ref>Potter, ''The Roman Empire at Bay'', p. 290.</ref> His every appearance was stage-managed.<ref>Southern, ''Severus to Constantine'', p. 163.</ref> This style of presentation was not new—many of its elements were first seen in the reigns of Aurelian and Severus—but it was only under the Tetrarchs that it was refined and made into an explicit system.<ref>Southern, ''Severus to Constantine'', pp. 153–54, 163.</ref>
===Administrative===
In keeping with his move from an ideology of republicanism to one of autocracy, Diocletian's council of advisers, his ''consilium'', differed from those of earlier emperors. He destroyed the Augustan illusion of imperial government as a cooperative affair between emperor, army, and Senate.<ref>Southern, ''Severus to Constantine'', pp. 162–63.</ref> In its place he established an effectively autocratic structure, a shift later epitomized in the institution's name: it would become a ''consistorium'' ("[[consistory]]"), not a council. Diocletian regulated his court by distinguishing separate departments (''scrina'') for different tasks.<ref>Southern, ''Severus to Constantine'', pp. 162–63; Williams, ''Diocletian'', p. 110.</ref> From this structure came the offices of different ''magistri'', like the ''Magister officiorum'' ("Master of offices"), and associated secretariats. These were men suited to dealing with petitions, requests, correspondence, legal affairs, and foreign embassies. Within his court Diocletian maintained a permanent body of legal advisers, men with significant influence on his re-ordering of juridical affairs. There were also two finance ministers, dealing with the separate bodies of the public treasury and the private domains of the emperor, and the praetorian prefect, the most significant person of the whole. Diocletian's reduction of the Praetorian Guards to the level of a simple city garrison for Rome lessened the civil powers of the office, but the office retained great power. The prefect kept a staff of hundreds and managed affairs in all segments of government: in taxation, administration, jurisprudence, and minor military commands, the praetorian prefect was often second only to the emperor himself.<ref>Williams, ''Diocletian'', p. 110.</ref> It has been estimated that under Diocletian the number of men in the [[civil service]] doubled from 15,000 men to 30,000 men.<ref name="civil">W. Treadgold, ''A History of the Byzantine State and Society'', 19</ref>
For a more efficient collection of taxes and supplies, and to ease the enforcement of the law, Diocletian doubled the number of [[Roman province|provinces]] from fifty to almost one hundred. The provinces were grouped into twelve [[Roman diocese|dioceses]], each governed by an appointed official called a ''[[vicarius]]'', or "deputy of the praetorian prefects".<ref>Barnes, ''Constantine and Eusebius'', p. 9.</ref> Some of the provincial divisions required revision, and were modified either soon after 293 or early in the fourth century.<ref name = "hcwmwc">Barnes, ''Constantine and Eusebius'', p. 10.</ref> The dissemination of imperial law to the provinces was facilitated under Diocletian's reign, because Diocletian's reform of the empire's provincial structure meant that there were now a greater number of governors ruling over smaller regions and smaller populations.<ref>Potter, ''The Roman Empire at Bay'', p. 296.</ref> Diocletian's reforms shifted the governors' main function to that of the presiding official in the lower courts:<ref>Harries, ''Law and Empire'', pp. 53–54; Potter, ''The Roman Empire at Bay'', p. 296.</ref> whereas in the early empire military and judicial functions were the function of governor, and [[Promagistrate|procurators]] had supervised taxation; under the new system ''vicarii'' and governors were responsible for justice and taxation, and a new class of ''[[Dux|duces]]'' ("[[duke]]s"), acting independently of the civil service, had military command. These dukes sometimes administered two or three of the new provinces created by Diocletian, and had forces ranging from two thousand to more than twenty thousand men.<ref>Barnes, ''Constantine and Eusebius'', pp. 9–10; Treadgold, ''Byzantine State and Society'', pp. 18–20.</ref>
===Legal===
[[Image:Digesto 02.jpg|thumb|upright|A 1581 reprint of the ''Digestorum'' from [[Justinian I|Justinian]]'s ''[[Corpus Juris Civilis]]'' (527–534). The ''Corpus'' drew on the codices of Gregorius and Hermogenianus, drafted and published under Diocletian's reign.]]
As with most emperors, much of Diocletian's daily routine rotated around legal affairs, responding to appeals and petitions, and delivering decisions. Rescripts, authoritative interpretations issued by the emperor in response to demands from disputants in both public and private cases, were a common duty of second- and third-century emperors. Diocletian was awash in paperwork, and was nearly incapable of delegating his duties. It would have been seen as a dereliction of duty to ignore them. Diocletian's praetorian prefects—Afranius Hannibalianus, Julius Asclepiodotus, and Flavius Constantius—aided in regulating the flow and presentation of such paperwork, but the deep legalism of Roman culture kept the workload heavy.<ref>Williams, ''Diocletian'', pp. 53–54, 142–43.</ref> Emperors in the forty years preceding Diocletian's reign had not managed these duties so effectively, and their output in attested rescripts is low. Diocletian, by contrast, was prodigious in his affairs: there are over 1,000 rescripts in his name still surviving, and these represent only a small portion of the total issue.<ref>Williams, ''Diocletian''. p. 143.</ref>
Under the governance of the [[jurist]]s Gregorius, Aurelius Arcadius Charisius, and Hermogenianus, the imperial government began issuing official books of [[precedent]], collecting and listing all the rescripts that had been issued from the reign of [[Hadrian]] (r. 117–138) to the reign of Diocletian.<ref>Harries, ''Law and Empire'', pp. 14–15; Potter, ''The Roman Empire at Bay'', pp. 295–96.</ref> The ''Codex Gregorianus'' includes rescripts up to 292, which the ''Codex Hermogenianus'' updated with a comprehensive collection of rescripts issued by Diocletian in 293 and 294.<ref name = "hcwmwc"/> The jurists themselves were generally conservative, and constantly looked to past Roman practice and theory for guidance.<ref>Harries, ''Law and Empire'', pp. 21, 29–30; Potter, ''The Roman Empire at Bay'', pp. 295–96.</ref> They were probably given a looser administrative structure than that imposed on the later compilers of the ''[[Codex Theodosianus]]'' (438) and ''[[Corpus Juris Civilis#Codex_Justinianus|Codex Justinianus]]'' (529). Their work lacked the rigid structuring of those later codes,<ref>Harries, ''Law and Empire'', pp. 21–22.</ref> and was not published in the name of the emperor, but in the names of its compilers.<ref>Harries, ''Law and Empire'', pp. 63–64.</ref> The compilers' codifications were radical in the decentralized Roman legal system.<ref>Potter, ''The Roman Empire at Bay'', pp. 295–96.</ref> There is a sharp increase in the number of edicts and rescripts produced under Diocletian's rule, a fact that has been read as evidence of the Diocletian's thoroughgoing effort to realign society on terms established by the imperial center.<ref>Potter, ''The Roman Empire at Bay'', pp. 296, 652.</ref>
After Diocletian's reform of the provinces, governors were often referred to by the name ''iudex'', or [[judge]]. The governor became responsible for his decisions first to his immediate superiors, as well as to the more distant office of the emperor.<ref>Harries, ''Law and Empire'', p. 162.</ref> It was most likely at this time that judicial records became verbatim accounts of what was said in trial, making it easier to determine bias or improper conduct on the part of the governor. With these records and the empire's universal right of [[appeal]], imperial authorities probably had a great deal of power to enforce behavior standards for their judges.<ref>Harries, ''Law and Empire'', p. 167.</ref> In spite of Diocletian's attempts at reform, the provincial restructuring was far from clear, especially when citizens appealed the decisions of their governors. Proconsuls, for example, were often both judges of first instance and appeal, and the governors of some provinces took appellant cases from their neighbors. It soon became impossible to avoid taking some cases to the emperor for arbitration and judgment.<ref>Harries, ''Law and Empire'', p. 55.</ref>
===Military===
It is archaeologically difficult to distinguish Diocletian's fortifications from those of his successors and predecessors. The Devil's Dyke, for example, Danubian earthworks traditionally attributed to Diocletian, cannot even be securely dated to a particular century. The most that can be said about built structures under Diocletian's reign is that he rebuilt forts along the Rhine-[[Iller]]-Danube line, in Egypt, and on the frontier with Persia. Beyond that, much discussion is speculative, and reliant on the broad generalizations of written sources. Diocletian and the Tetrarchs had no consistent plan for frontier advancement, and records of raids and forts built across the frontier are likely to indicate only temporary claims. The ''Strata Diocletiana'' along the eastern frontier is the classic Diocletianic frontier system, consisting of an outer road followed by tightly spaced forts followed by further fortifications in the rear.<ref>Southern, ''Severus to Constantine'', pp. 154–55. See also: Williams, ''Diocletian'', pp. 91–101.</ref>
Lactantius criticized Diocletian for an excessive increase in troop sizes, declaring that "each of the four [Tetrarchs] strove to have a far larger number of troops than previous emperors had when they were governing the state alone".<ref>Lactantius, ''DMP'' 7.2, qtd. in Corcoran, "Before Constantine", p. 46.</ref> The fifth-century pagan [[Zosimus]], by contrast, praised Diocletian for keeping troops on the borders, rather than keeping them in the cities, as Constantine was held to have done.<ref>Zosimus, 2.34 qtd. in Corcoran, "Before Constantine", p. 46.</ref> Both these views had some truth to them, despite the biases of their authors: Diocletian and the Tetrarchs did greatly expand the army, and the growth was mostly in frontier regions, although it is difficult to establish the precise details of these shifts given the weakness of the sources.<ref>Southern, ''Severus to Constantine'', p. 157; Treadgold, ''Byzantine State and Society'', p. 19.</ref> The army expanded to about 581,000 men from a 285 strength of 390,000 men. The growth was smaller in the East, which only expanded from 253,000 men to 311,000 men, most of whom manned the Persian frontier. The navy's forces increased from approximately 46,000 men to approximately 64,000 men.<ref>Treadgold, ''Byzantine State and Society'', p. 19.</ref>
Diocletian's increases in the size of the civil service and the military forces of his empire meant that the empire's tax burden would also increase, especially given how the military was the largest burden on the imperial budget.<ref>Southern, ''Severus to Constantine'', p. 158; Treadgold, ''Byzantine State and Society'', pp. 112–13.</ref> The proportion of the adult male population serving in the army increased from roughly 1 in 25 to 1 in 15, an increase judged excessive by some modern commentators. Official troop allowances were kept to low levels, and the mass of troops often resorted to extortion or the taking of civilian jobs.<ref name = "lpnxzn">Southern, ''Severus to Constantine'', p. 159; Treadgold, ''Byzantine State and Society'', pp. 112–13.</ref> Arrears became the norm for most troops. Many were even given payment in kind in place of their salaries.<ref name="SSC159">Southern, ''Severus to Constantine'', p. 159.</ref> Were he unable to pay for his enlarged army, there would likely be civil conflict, potentially open revolt. Diocletian was led to devise a new system of taxation.<ref name = "lpnxzn"/>
===Economic===
====Taxation====
Diocletian introduced an extensive new tax system based on heads (''capita'') and land (''iuga'') and tied to a new, regular census of the empire's population and wealth. Census officials traveled throughout the empire, assessed the value of labor and land for each landowner, and joined the landowners' totals together to make city-wide totals of ''capita'' and ''iuga''.<ref name="TBSS20">Treadgold, ''Byzantine State and Society'', p. 20.</ref> The ''iugum'' was not a consistent measure of land, but varied according to the type of land and crop, and the amount of labor necessary for sustenance. The ''caput'' was not consistent either: women, for instance, were often valued at half a ''caput'', and sometimes at other values.<ref name="SSC159"/> The city would provide animals, money, and manpower in proportion to its ''capita'', and grain in proportion to its ''iuga''.<ref name="TBSS20"/>
Most taxes were due on each [[September 1]], and levied from individual landowners by ''[[Decurion (administrative)|decuriones]]'' (decurions). These decurions, analogous to city councilors, were responsible for paying from their own pocket what they failed to collect from the populace.<ref name = "sfirim">Southern, ''Severus to Constantine'', p. 160; Treadgold, ''Byzantine State and Society'', p. 20.</ref> Diocletian's reforms also increased the number of financial officials in the provinces: more ''rationales'' and ''magistri privatae'' are attested under Diocletian's reign than before. These offices were to manage imperial properties and to supervise the collection of revenue.<ref name = "hcwmwc"/> Despite the instability of the coinage, most taxes were either levied in or convertible into money. Rates shifted to take inflation into account.<ref name="TBSS20"/> In 296, Diocletian issued an edict reforming census procedures. This edict introduced a general five-year census for the whole empire, replacing prior censuses that had operated at different speeds throughout the empire. The new censuses would keep up with changes in the values of ''capita'' and ''iuga''.<ref>Potter, ''The Roman Empire at Bay'', p. 333.</ref> In the interests of securing a generally egalitarian tax system, Italy, which had long been exempt from taxes, was exempt no longer. Save for the city of Rome and a region extending one hundred miles in every direction from the city center (the [[Suburbicarian diocese]]s), Italy would now be taxed on the same level as any other province.<ref>Barnes, ''Constantine and Eusebius'', p. 9, 288; Southern, ''Severus to Constantine'', p. 159.</ref>
Diocletian's edicts emphasize the common liability of all taxpayers. Public records of all taxes were established to enhance the transparency of the operation, so that taxpayers would know exactly how much their neighbors paid.<ref>Williams, ''Diocletian'', p. 125.</ref> The position of ''decurion'' had long been an honor sought by wealthy aristocrats, but under Diocletian its tax-collecting requirements became much more rigorous. Decurions and the city treasury could be bankrupted if production figures fell.<ref name = "sfirim"/> The effects of the new tax system were deeply felt: boundary-markers (necessary for tax administration) dating from the Tetrarchic period make relatively frequent appearances in Near-Eastern towns, even in remote country districts like Sakkaia in the northern [[Hauran]].<ref>''Supplementum Epigraphicum Graecum'' VII, no. 1055; Millar, ''Roman Near East'', pp. 193–96.</ref> The Roman populace, long accustomed to irregular and ineffective tax collection, went through an uncomfortable period of adjustment to Diocletian's reforms. But even the lower classes were able to pay this burden.<ref>Brown, ''Rise of Christendom'', p. 57; Williams, ''Diocletian'', p. 123.</ref> The common benefits of the new system were clear: taxes were predictable, regular, and fair, and the population was now free from fear. Citizens of the fourth century, safe behind the frontiers established and paid for by their taxes, no longer had to fear foreign occupation.<ref>Williams, ''Diocletian'', p. 124.</ref>
====Currency and inflation====
[[Image:Edict on Maximum Prices Diocletian piece in Berlin.jpg|thumb|A fragment of the ''[[Edict on Maximum Prices]]'' (301), on display in [[Berlin]]]]
By the early 280s, market forces had created a stable exchange rate between gold and the copper ''[[antoninianus]]'', more or less stablizing commodity prices. The ''antoninianus'', which had become the standard medium of exchange, was valued at one sixty-thousandth the value of a pound of gold.<ref name="POTBAY392">Potter, ''The Roman Empire at Bay'', p. 392.</ref> But inflation remained a serious issue.<ref name="SSC160">Southern, ''Severus to Constantine'', p. 160.</ref> In the wake of a brief period of re-inflation, Diocletian began a more comprehensive reform of the currency in 293.<ref name="POTBAY392"/> The new system consisted of five coins: the ''aureus''/''[[solidus]]'', a gold coin weighing, like its predecessors, one-sixtieth of a pound; the ''[[argenteus]]'', a coin weighing one ninety-sixth of a pound and containing ninety-five percent pure silver; the ''[[follis]]'', sometimes referred to as the ''laureatus'' A, which is a copper coin with added silver struck at the rate of thirty-two to the pound; the ''radiatus'', a small copper coin struck at the rate of 108 to the pound, with no added silver; and a coin known today as the ''laureatus'' B, a smaller copper coin struck at the rate of 192 to the pound.<ref>Potter, ''The Roman Empire at Bay'', pp. 392–93.</ref> The ''[[denarius]]'' was dropped from the imperial mints,<ref name="SSC160"/> though the values of new coins continued to be measured in reference to it.<ref name="POTBAY392"/>
By 301, however, the system was in trouble, strained by a new bout of inflation. Diocletian therefore issued his ''Edict on Coinage'', an act re-tariffing all debts so that the ''nummii'', the most common coin in circulation, would be worth half as much.<ref>Potter, ''The Roman Empire at Bay'', pp. 334, 393; Southern, ''Severus to Constantine'', p. 160.</ref> In the edict, preserved in an inscription from the city of [[Aphrodisias]] in [[Caria]] (near [[Geyre]], Turkey), it was declared that all debts contracted before [[September 1]] [[301]] would be repaid at the old standards, while all debts contracted after September 1 would be repaid at the new standards.<ref name="POTBAY33435">Potter, ''The Roman Empire at Bay'', pp. 334–35.</ref> It appears that the edict was made in an attempt to preserve the current price of gold and to keep the empire's coinage on silver, Rome's traditional metal currency.<ref>Potter, ''The Roman Empire at Bay'', p. 393.</ref>
The ''[[Edict on Maximum Prices]]'' (''Edictum De Pretiis Rerum Venalium'' in Latin) was issued two to three months after the coinage edict,<ref name="SSC160"/> somewhere between [[November 20]] and [[December 10]] [[301]].<ref name="POTBAY33435"/> It survives in many different versions, written on wood, papyrus, and stone.<ref>Southern, ''Severus to Constantine'', pp. 160, 339.</ref> It is the best-preserved Latin inscription surviving from the Greek East.<ref>Potter, ''The Roman Empire at Bay'', p. 336.</ref> In the edict, Diocletian declared that the current pricing crisis resulted from the unchecked greed of merchants, and had resulted in turmoil for the mass of common citizens. The language of the edict calls on the people's memory of their benevolent leaders, and exhorts them to enforce the provisions of the edict, and thereby restore perfection to the world. The edict goes on to list in detail over one thousand goods and accompanying retail prices not to be exceeded. Penalties are laid out for various pricing transgressions.<ref>Potter, ''The Roman Empire at Bay'', p. 335; Southern, ''Severus to Constantine'', p. 161.</ref>
In the most basic terms, the edict was ignorant of the law of [[supply and demand]]; it ignored the fact that prices might vary from region to region, or according to product availability, and it ignored the impact of transportation costs in the retail pricing of goods. In the judgment of the historian David Potter, the edict was "an act of economic lunacy".<ref>Potter, ''The Roman Empire at Bay'', p. 335.</ref> The edict's penalties were applied unevenly across the empire, widely resisted, and eventually dropped, perhaps within a year of the edict's issue.<ref>Potter, ''The Roman Empire at Bay'', p. 336; Southern, ''Severus to Constantine'', p. 161.</ref> Lactantius has written of the perverse accompaniments to the edict; of goods withdrawn from the market, of brawls over minute variations in price, of the deaths that came when its provisions were enforced. His account may be true, but it seems to modern historians exaggerated and hyperbolic,<ref>Lactantius, ''DMP'' 7.6–7; Southern, ''Severus to Constantine'', p. 161.</ref> and the impact of the law is recorded in no other ancient source.<ref>Potter, ''The Roman Empire at Bay'', p. 336; Williams, ''Diocletian'', pp. 131–32.</ref>
==Legacy==
The historian [[A.H.M. Jones]] observed that "It is perhaps Diocletian's greatest achievement that he reigned twenty-one years and then abdicated voluntarily, and spent the remaining years of his life in peaceful retirement."<ref>Jones, ''Later Roman Empire'', p. 40.</ref> Diocletian was one of the few emperors of the third and fourth centuries to die naturally, and the first in the history of the empire to retire voluntarily.<ref>Williams, ''Diocletian'', pp. 228–29.</ref> Once he retired, however, his Tetrarchic system collapsed. Without the guiding hand of Diocletian, the empire frequently broke into civil war. Only in 324, when Constantine alone emerged triumphant, did stability return.<ref>Williams, ''Diocletian'', pp. 196–98.</ref> Under the Christian Constantine, all of Diocletian's achievements were repudiated. Constantine's rule, however, validated Diocletian's achievements and the autocratic principle he represented:<ref>Williams, ''Diocletian'', p. 204.</ref> the borders remained secure, in spite of Constantine's large expenditure of forces during his civil wars; the bureaucratic transformation of Roman government was completed; and Constantine made Diocletian's court ceremonies even more extravagant.<ref>Williams, ''Diocletian'', pp. 205–6.</ref>
Constantine abandoned Diocletian's aim of preserving a stable silver coinage, and minted instead a new gold ''solidus''.<ref>Williams, ''Diocletian'', pp. 207–8.</ref> Diocletian's paganism was repudiated in favor of an imperially sponsored Christianity; his attempts at controlling prices ignored. But even Christianity became tied to the state structure of the Roman Empire in an autocratic way; Constantine claimed for himself the same close relationship with the Christian God as Diocletian had claimed with Jupiter.<ref>Williams, ''Diocletian'', p. 206.</ref> Most importantly, Diocletian's tax system was preserved and tightened.<ref>Williams, ''Diocletian'', p. 208.</ref> Aided by the new state machinery introduced by Diocletian, the [[Byzantine Empire]] would last for over one thousand years after his death.<ref>Williams, ''Diocletian'', pp. 218–19.</ref>
==Notes==
{{reflist|3}}
==References==
===Primary sources===
<div class="references-small">
* ''[[Epitome de Caesaribus]]'' ([http://www.roman-emperors.org/epitome.htm translation]) ''ca''. 395.
* [[Eutropius]], ''Breviarium ab Urbe Condita'' (''Abbreviated History from the City's Founding'') ''ca''. 369. [http://www.forumromanum.org/literature/eutropius/trans9.html Book IX]
* [[Lactantius]], ''[http://www.acs.ucalgary.ca/~vandersp/Courses/texts/lactant/lactperf.html Liber De Mortibus Persecutorum]'' (''Book on the Deaths of the Persecutors'') ''ca''. 313–15.
* [[Joannes Zonaras]], ''Compendium of History'' (Επιτομή Ιστορίων) ''ca''. 1200. [http://www.ancientsites.com/aw/Post/1050581 Compendium extract: Diocletian to the Death of Galerius: 284–311]
</div>
===Secondary sources===
<div class="references-small">
* Banchich, Thomas M. "[http://www.roman-emperors.org/iulian.htm Iulianus (''ca''. 286–293 A.D.)]." ''De Imperatoribus Romanis'' (1997). Accessed March 8, 2008.
* [[Timothy Barnes|Barnes, Timothy D.]] "Lactantius and Constantine." ''The Journal of Roman Studies'' 63 (1973): 29–46.
* Barnes, Timothy D. "Two Senators under Constantine." ''The Journal of Roman Studies'' 65 (1975): 40–49.
* Barnes, Timothy D. "Sossianus Hierocles and the Antecedents of the "Great Persecution"." ''The Journal of Roman Studies'' 80 (1976): 239–52.
* Barnes, Timothy D. ''Constantine and Eusebius''. Cambridge, MA: Harvard University Press, 1981. ISBN 978-0674165311
* Barnes, Timothy D. ''The New Empire of Diocletian and Constantine''. Cambridge, MA: Harvard University Press, 1982. ISBN 0783722214
* Bleckmann, Bruno. "Diocletianus." In ''Brill's New Pauly, Volume 4'', edited by Hubert Cancik and Helmut Schneider, 429–38. Leiden: Brill, 2002. ISBN 9004122591
* Bowman, Alan K. "Diocletian and the First Tetrarchy." In ''The Cambridge Ancient History, Volume XII: The Crisis of Empire'', edited by Alan Bowman, Averil Cameron, and Peter Garnsey, 67–89. Cambridge University Press, 2005. ISBN 0-521-30199-8
* [[Peter Brown (historian)|Brown, Peter]]. ''The Rise of Western Christendom''. Oxford: Blackwell Publishing, 2003. ISBN 0-631-22138-7
* Burgess, R.W. "The Date of the Persecution of Christians in the Army". ''Journal of Theological Studies'' 47:1 (1996): 157–158.
* Corcoran, Simon. "Before Constantine." In ''The Cambridge Companion to the Age of Constantine'', edited by Noel Lenski, 35–58. New York: Cambridge University Press, 2006. Hardcover ISBN 0-521-81838-9 Paperback ISBN 0-521-52157-2
* DiMaio, Jr., Michael. "[http://www.roman-emperors.org/chlorus.htm Constantius I Chlorus (305–306 A.D.)]." ''De Imperatoribus Romanis'' (1996a). Accessed March 8, 2008.
* DiMaio, Jr., Michael. "[http://www.roman-emperors.org/galerius.htm Galerius (305–311 A.D.)]." ''De Imperatoribus Romanis'' (1996b). Accessed March 8, 2008.
* DiMaio, Jr., Michael. "[http://www.roman-emperors.org/domach.htm L. Domitius Domitianus and Aurelius Achilleus (''ca''.296/297–''ca''.297/298)]." ''De Imperatoribus Romanis'' (1996c). Accessed March 8, 2008.
* DiMaio, Jr., Michael. "[http://www.roman-emperors.org/maxherc.htm Maximianus Herculius (286–305 A.D)]." ''De Imperatoribus Romanis'' (1997). Accessed March 8, 2008.
* Elliott, T. G. ''The Christianity of Constantine the Great''. Scranton, PA: University of Scranton Press, 1996. ISBN 0-940866-59-5
* Harries, Jill. ''Law and Empire in Late Antiquity''. Cambridge: Cambridge University Press, 1999. Hardcover ISBN 0-521-41087-8 Paperback ISBN 0-521-42273-6
* Helgeland, John. "Christians and the Roman Army A.D. 173-337." ''Church History'' 43:2 (1974): 149–163, 200.
* Jones, A.H.M. ''The Later Roman Empire, 284–602: A Social, Economic and Administrative Survey''. Baltimore: Johns Hopkins University, 1986.
* Leadbetter, William. "[http://www.roman-emperors.org/carus.htm Carus (282–283 A.D.)]." ''De Imperatoribus Romanis'' (2001a). Accessed February 16, 2008.
* Leadbetter, William. "[http://www.roman-emperors.org/numerian.htm Numerianus (283–284 A.D.)]." ''De Imperatoribus Romanis'' (2001b). Accessed February 16, 2008.
* Leadbetter, William. "[http://www.roman-emperors.org/carinus.htm Carinus (283–285 A.D.)]." ''De Imperatoribus Romanis'' (2001c). Accessed February 16, 2008.
* Lewis, Naphtali, and Meyer Reinhold. ''Roman Civilization: Volume 2, The Roman Empire''. New York: Columbia University Press, 1990. ISBN 0-231-07133-7
* Liebeschuetz, J. H. W. G. ''Continuity and Change in Roman Religion''. Oxford: Oxford University Press, 1979. ISBN 0-19-814822-4.
* Mackay, Christopher S. "Lactantius and the Succession to Diocletian." ''Classical Philology'' 94:2 (1999): 198–209.
* Mathisen, Ralph W. "[http://www.roman-emperors.org/dioclet.htm Diocletian (284–305 A.D.)]." ''De Imperatoribus Romanis'' (1997). Accessed February 16, 2008.
* [[Fergus Millar|Millar, Fergus]]. ''The Roman Near East, 31 B.C.–A.D. 337''. Cambridge, MA: Harvard University Press, 1993. Hardcover ISBN 0-674-77885-5 Paperback ISBN 0-674-77886-3
* Odahl, Charles Matson. ''Constantine and the Christian Empire''. New York: Routledge, 2004. Hardcover ISBN 0-415-17485-6 Paperback ISBN 0-415-38655-1
* Potter, David S. ''The Roman Empire at Bay: AD 180–395''. New York: Routledge, 2005. Hardcover ISBN 0-415-10057-7 Paperback ISBN 0-415-10058-5
* Rees, Roger. ''Layers of Loyalty in Latin Panegyric: AD 289–307''. New York: Oxford University Press, 2002. ISBN 0-19-924918-0
* Rees, Roger. ''Diocletian and the Tetrarchy''. Edinburgh: Edinburgh University Press, 2004. ISBN 0-7486-1661-6
* [[Michael Rostovtzeff|Rostovtzeff, Michael]]. ''The Social and Economic History of the Roman Empire''. Oxford: Oxford University Press, 1966. ISBN 978-0198142317
* Southern, Pat. ''The Roman Empire from Severus to Constantine''. New York: Routledge, 2001. ISBN 0-415-23944-3
* Treadgold, Warren. ''A History of the Byzantine State and Society''. Stanford: Stanford University Press, 1997. ISBN 0-8047-2630-2
* Williams, Stephen. ''Diocletian and the Roman Recovery''. New York: Routledge, 1997. ISBN 0-415-91827-8
</div>
==See also==
* [[20,000 Martyrs of Nicomedia]]
* ''[[Dioclesian]]'', [[Henry Purcell]]'s 1690 tragicomic semi-opera, loosely based on the life of the historical Diocletian
==External links==
{{Commons|Diocletian}}
*[http://www.newadvent.org/cathen/05007b.htm Diocletian] from the ''[[Catholic Encyclopedia]]''.
*[http://www.anders.com/lectures/lars_brownworth/12_byzantine_rulers/ 12 Byzantine Rulers], by [[Lars Brownworth]]. 15 minute audio lecture on Diocletian.
*[http://digital.library.wisc.edu/1711.dl/DLDecArts.AdamRuins Ruins of the Palace of the Emperor Diocletian at Spalatro in Dalmatia] By Robert Adam, 1764. Plates made available by the [[University of Wisconsin–Madison|University of Wisconsin]] Digital Collections Center. (N.B. "Spalatro" was a less used alternative form of "Spalato", the Italian name for Croatian "Split").
{{Roman Emperor | Prev=[[Numerian]] '''and''' [[Carinus]]| CoEmperor=with [[Maximian]] <small>(286–305)</small>| Next=[[Constantius Chlorus]]'''<br />and '''[[Galerius]]|years=284–305}}
{{start box}}
{{succession box|
title=[[Roman consul|Consul suffectus]]|
before=[[Carus]], [[Carinus]]|
years=284, with Bassus |
after=Carinus, T. Claudius M. Aurelius Aristobulus |
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{{succession box|
title=[[Roman consul|Consul suffectus]]|
before=[[Carus]], [[Numerian]]|
years=285 |
after=Marcus Iunius Maximus, Vettius Aquilinus |
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{{succession box|
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years=287, with [[Maximian]] |
after=Maximian, Pomponius Ianuarianus |
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{{succession box|
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{{succession box|
title=[[Roman consul|Consul]]|
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years=293, with Maximian |
after=[[Constantius Chlorus|Constantius]], [[Galerius]] |
}}
{{succession box|
title=[[Roman consul|Consul]]|
before=Nummius Tuscus, Gaius Annius Anullinus|
years=296, with Constantius |
after=Maximian, Galerius |
}}
{{succession box|
title=[[Roman consul|Consul]]|
before=[[Sextus Anicius Faustus Paulinus (I)|Sextus Anicius Faustus Paulinus]], Virius Gallus|
years=299, with Maximian |
after=Constantius, Galerius |
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{{succession box|
title=[[Roman consul|Consul]]|
before=Constantius, Galerius|
years=303, with Maximian |
after=Diocletian, Maximian |
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{{succession box|
title=[[Roman consul|Consul]]|
before=Diocletian, Maximian|
years=304, with Maximian |
after=Constantius, Galerius |
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{{succession box|
title=[[Roman consul|Consul]] in the East and the West|
before=[[Maximinus]] (in the East); Maximian and [[Constantine I|Constantine]] (in the West)|
years=308, with Galerius<br/><small>From 307 to 313, different consuls are attested in the regions administered by Galerius (the East), Constantine (the West), and [[Maxentius]] (Italy). Diocletian is attested only in the domains of Constantine and Galerius.</small> |
after=[[Licinius]] and Constantine (in the East); ''post consulatum X et VII'' (in the West)|
}}
{{end box}}
{{Roman Emperors}}
{{featured article}}
[[Category:Roman emperors]]
[[Category:Constantinian dynasty]]
[[Category:Crisis of the Third Century]]
[[Category:Late Antiquity]]
[[Category:Deified Roman emperors]]
[[Category:Ancient Roman adoptive parents]]
[[Category:245 births]]
[[Category:311 deaths]]
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