Editing Diocletian (section)

==Tetrarchy==
{{see also|Tetrarchy}}

===Foundation of the Tetrarchy===
[[File:Tetrarchy map3.jpg|thumb|Map of the Tetrarchy in 293, showing the [[Roman diocese|dioceses]] and the four tetrarchs' zones of influence.<ref>[https://www.worldhistory.org/image/18530/the-roman-empire-and-the-tetrarchy-of-diocletian-2/ The Roman Empire and the Tetrarchy of Diocletian, 293 - 305 CE], ''[[World History Encyclopedia]]''</ref>]]
[[File:Sbeitla 10.jpg|thumb|Triumphal arch of the Tetrarchy, [[Sbeitla]], [[Tunisia]]]]
Some time after his return, and before 293, Diocletian transferred command of the war against Carausius from Maximian to [[Constantius Chlorus|Flavius Constantius]], who concluded it successfully in 296.  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 1 March 293 at Milan, Maximian gave Constantius the office of ''Caesar''.{{sfnm|1a1=Barnes|1y=1981|1pp=8–9|2a1=Barnes|2y=1982|2pp=4, 36–37|3a1=Potter|3y=2005|3p=288|4a1=Southern|4y=2001|4p=146|5a1=Williams|5y=1985|5pp=64–65; 73–74}} The same day, in either Philippopolis ([[Plovdiv]], [[Bulgaria]]) or Sirmium, Diocletian did the same for [[Galerius|Galerius Maximianus]], husband to Diocletian's daughter Valeria, and perhaps Diocletian's praetorian prefect.{{refn|The contemporary [[Lactantius]] gives 1 March,{{sfn|Lactantius|loc=35}} while the 7th-century [[Chronicon Paschale]] gives 21 May.<ref>[[Chronicon Paschale]] [https://archive.org/details/chronicon-p/page/2/mode/1up O. 268]</ref> Still, not all authors agree on the exact date.{{sfnm|1a1=Barnes|1y=1981|1pp=8–9|2a1=Barnes|2y=1982|2p=4, 38|3a1=Potter|3y=2005|3p=288|4a1=Southern|4y=2001|4p=146|5a1=Williams|5y=1985|5pp=64–65}}|group="Note"}} Constantius was assigned Gaul and Britain. Galerius was initially assigned Syria, Palestine, Egypt, and responsibility for the eastern borderlands.{{sfnm|1a1=Barnes|1y=1981|1pp=8–9|2a1=Williams|2y=1985|2p=67}}

This arrangement is called the [[Tetrarchy]], from a [[Ancient Greek|Greek]] term meaning "rulership by four".{{sfn|Southern|2001|p=145}} The Tetrarchs were more or less sovereign in their own lands, and they travelled with their own imperial courts, administrators, secretaries, and armies.{{sfnm|1a1=Corcoran|1y=2006|1pp= 45–46|2a1=Williams|2y=1985|2p=67}} They were joined by blood and marriage; Diocletian and Maximian now styled themselves as brothers, and formally adopted Galerius and Constantius as sons. These relationships implied a line of succession. Galerius and Constantius would become ''Augusti'' after the departure of Diocletian and Maximian. Maximian's son [[Maxentius]] and Constantius's son [[Constantine I|Constantine]] would then become ''caesares''. In preparation for their future roles, Constantine and Maxentius were taken to Diocletian's court in Nicomedia.{{sfn|Barnes|1981|pp=8–9}}

===Conflict in the Balkans and Egypt===
[[File:Philae, Trajan's Kiosk, Aswan, Egypt, Oct 2004.jpg|thumb|A [[Trajan]]ic temple on the island of [[Philae]], the newly established border between the [[Nobatae]] and [[Blemmyes]] and [[Roman Egypt]]{{sfn|Barnes|1981|pp=17–18}}]]
Diocletian spent the spring of 293 travelling with Galerius from Sirmium ([[Sremska Mitrovica]], [[Serbia]]) to [[Byzantium]] ([[Istanbul]], [[Turkey]]). Diocletian then returned to Sirmium, where he remained for the following winter and spring. He campaigned successfully against the Sarmatians in 294, probably in the autumn.{{sfn|Odahl|2004|p=59}} The Sarmatians' defeat kept them from the Danube provinces for a long time. Meanwhile, Diocletian built forts north of the Danube,{{sfnm|1a1=Barnes|1y=1981|1p=17|2a1=Williams|2y=1985|1pp=76–77}} part of a new defensive line called the ''Ripa Sarmatica'', at [[Aquincum]] ([[Budapest]], [[Hungary]]), Bononia ([[Vidin]], Bulgaria), Ulcisia Vetera, Castra Florentium, Intercisa ([[Dunaújváros]], Hungary), and Onagrinum ([[Begeč]], Serbia).{{sfn|Williams|1985|p=76}} In 295 and 296 Diocletian campaigned in the region again, and won a victory over the Carpi in the summer of 296.{{sfnm|1a1=Barnes|1y=1981|1p=17|2a1=Odahl|2y=2004|2p=59|3a1=Southern|3y=2001|3pp=149–150}} Later during both 299 and 302, as Diocletian was residing in the East, it was Galerius's turn to campaign victoriously on the Danube. 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; an inscription at [[Sexaginta Prista]] on the Lower Danube extolled restored tranquility to the region.{{sfn|Carrié|Rousselle|1999|pp=163–164}} The defense came at a heavy cost but was a significant achievement in an area difficult to defend.{{sfn|Williams|1985|p=77}}
[[File:Roman fresco on the southern wall of the cult chamber in Luxor temple depicting dignitaries revering the emperor, 4th century AD, Egypt.jpg|thumb|Roman fresco on the southern wall of [[Luxor Temple|Luxor Temple's]] imperial cult chamber. It depicts senior military officers gathered around Diocletian's throne, circa 280.<ref>{{Cite web |title=Chapel of Imperial Cult |url=https://madainproject.com/chapel_of_imperial_cult |access-date=24 December 2023 |website=Madain Project |language=en}}</ref><ref>{{Cite book |last1=Davenport |first1=Caillan |url=https://books.google.com/books?id=ycbYEAAAQBAJ |title=The Roman Imperial Court in the Principate and Late Antiquity |last2=McEvoy |first2=Meaghan |date=23 January 2024 |publisher=Oxford University Press |isbn=978-0-19-286523-6 |pages=86–87 |language=en}}</ref>]]
Galerius, meanwhile, was engaged during 291–293 in disputes in [[Upper Egypt]], where he suppressed a regional uprising.{{sfn|Carrié|Rousselle|1999|pp=163–164}} He returned to Syria in 295 to fight the revanchist Persian empire.{{sfn|Barnes|1981|p=17}} Diocletian's attempts to bring the Egyptian tax system in line with Imperial standards stirred discontent, and a revolt swept the region after Galerius's departure.{{sfnm|1a1=Barnes|1y=1981|1p=17|2a1=Southern|2y=2001|2pp=160, 338}} The usurper [[Domitius Domitianus]] declared himself ''Augustus'' in July or August 297. Much of Egypt, including [[Alexandria]], recognized his rule.{{sfn|Barnes|1981|p=17}} Diocletian moved into Egypt to suppress him, first putting down rebels in the [[Thebaid]] in the autumn of 297,{{sfn|Odahl|2004|p=59}} then moving on to besiege Alexandria. Domitianus died in December 297,{{sfn|DiMaio|1997}} by which time Diocletian had secured control of the Egyptian countryside. Alexandria, whose defense was organized under Domitianus's former ''[[Corrector#Roman Antiquity|corrector]]'' [[Aurelius Achilleus]], held out probably until March 298.{{sfn|Barnes|1981|p=17}}{{sfn|DiMaio|1997}} Later in 298, the [[triumphal column]] now known as [[Pompey's Pillar (column)|Pompey's Pillar]] was erected in Alexandria to honor Diocletian.{{sfn|Delbrück|2007|pp=100–101}}

Bureaucratic affairs were completed during Diocletian's stay:{{sfnm|1a1=Barnes|1y=1981|1pp=17–18|2a1=Southern|2y=2001|2p=150}} a census took place, and Alexandria, in punishment for its rebellion, lost the ability to mint independently.{{sfn|Southern|2001|p=150}} Diocletian's reforms in the region, combined with those of [[Septimius Severus]], brought Egyptian administrative practices much closer to Roman standards.{{sfn|Harries|1999|p=173}} Diocletian travelled south along the Nile the following summer, where he visited [[Oxyrhynchus]] and [[Elephantine]].{{sfn|Southern|2001|p=150}} 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 with Galerius in Mesopotamia.{{sfn|Barnes|1981|pp=17–18}}

===War with Persia===
{{see also|Roman–Iranian relations|Roman–Persian Wars}}

====Invasion, counterinvasion====
[[File:Diocletian medallion.jpg|thumb|left|Medallion of Diocletian, AD&nbsp;294]]
In 294, [[Narseh]], a son of Shapur who had been passed over for the Sassanid succession, came to power in Persia.{{sfnm|1a1=Potter|1y=2005|1p=292|2a1=Williams|2y=1985|2p=69}} In early 294, Narseh sent Diocletian the customary package of gifts between the empires, and Diocletian responded with an exchange of ambassadors. Within Persia, Narseh was destroying every trace of his immediate predecessors from public monuments. He sought to identify himself with the warlike kings [[Ardashir I]] (r. 226–241) and [[Shapur I]] (r. 241–272), who had defeated and imprisoned Emperor [[Valerian (emperor)|Valerian]] (r. 253–260) following his failed invasion of the [[Sasanian Empire]].{{sfn|Williams|1985|pp=69–70}}

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</ref>{{sfnm|1a1=Barnes|1y=1981|1p=17|2a1=CAH|2p= 81|3a1=Potter|3y=2005|3p=292|4a1=Southern|4y=2001|4p=149}} He moved south into Roman Mesopotamia in 297, where he inflicted a severe defeat on Galerius in the region between Carrhae ([[Harran]], Turkey) and Callinicum ([[Raqqa]], Syria), suggested by the historian [[Fergus Millar]] to have been somewhere on the [[Balikh River]].{{sfnm|1a1=Eutropius|1loc=9.24–25|2a1=Barnes|2y=1981|2p=17|3a1=CAH|3p=81|4a1=Millar|4y=1993|4pp=177–178}}  Diocletian may or may not have been present at the battle,{{sfn|Potter|2005|p=652}} 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 (historian)|Eutropius]] 9.24–25; [[Theophanes Confessor]], [https://archive.org/details/ByzantineAndNearEasternHistoryAD284813/page/n55/mode/1up AM 5793].</ref>{{sfnm|1a1=Barnes|1y=1981|1p=17|2a1=CAH|2p=81|3a1=Potter|3y=2005|3pp=292–293}}{{refn|It is possible that Galerius's position at the head of the caravan was merely the conventional organization of an imperial progression, designed to show a caesar's deference to his augustus, and not an attempt to humiliate him.{{sfn|Rees|2004|p=14}}|group="Note"}}

[[File:Arch-of-Galerius-1.jpg|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{{sfn|Rees|2004|p=14}}{{sfn|Southern|2001|p=151}}]]
Galerius was reinforced, probably in the spring of 298, by a new contingent collected from the empire's Danubian holdings.{{sfnm|1a1=Barnes|1y=1981|1p=18|2a1=CAH|2p=81|3a1=Millar|3y=1993|3p=178}} Narseh did not advance from Armenia and Mesopotamia, leaving Galerius to lead the offensive in 298 with an attack on northern Mesopotamia via Armenia.{{sfnm|1a1=Millar|1y=1993|1p=178|2a1=Potter|2y=2005|2p=293}}{{refn|[[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.{{sfn|CAH|p=81}}|group="Note"}} It is unclear if Diocletian was present to assist the campaign; he might have returned to Egypt or Syria.{{refn|Lactantius criticizes Diocletian for his absence from the front,{{sfn|Lactantius|loc=9.6}} but Southern, dating Diocletian's African campaigns one year earlier than Barnes, places Diocletian on Galerius's southern flank.{{sfn|Southern|2001|pp=151, 335–336}}|group="Note"}} Narseh retreated to Armenia to fight Galerius's force, putting himself at a disadvantage; the rugged Armenian terrain was favorable to Roman infantry, but not to Sassanid cavalry. In two battles, Galerius won major victories over Narseh. During the [[Battle of Satala (298)|second encounter]], Roman forces seized Narseh's camp, his treasury, his harem, and his wife.{{sfnm|1a1=Barnes|1y=1981|1p=18|2a1=Potter|2y=2005|2p=293}} Galerius continued down the Tigris, and took the Persian capital Ctesiphon before returning to Roman territory along the Euphrates.{{sfnm|1a1=Barnes|1y=1981|1p=18|2a1=Millar|2y=1993|2p=178}}

====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 dismissed him.{{sfn|Barnes|1981|p=18}} Serious peace negotiations began in the spring of 299. The ''magister memoriae'' (secretary) of Diocletian and Galerius, Sicorius Probus, was sent to Narseh to present terms.{{sfn|Barnes|1981|p=18}} The conditions of the resulting [[Peace of Nisibis (299)|Peace of Nisibis]] were heavy:{{sfn|Potter|2005|p=293}}  Armenia returned to Roman domination, with the fort of Ziatha as its border; [[Kingdom of Iberia (antiquity)|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: [[Angeghtun|Ingilene]], Sophanene ([[Sophene]]), Arzanene ([[Aghdznik]]), [[Corduene]] (Carduene), and Zabdicene (near modern [[Hakkâri (city)|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.{{sfnm|1a1=Millar|1y=1993|1pp=178–179|2a1=Potter|2y=2005|2p=293}}

A stretch of land containing the later strategic strongholds of Amida ([[Diyarbakır]], Turkey) and [[Bezabde]] came under firm Roman military occupation.{{sfn|Millar|1993|p=178}} 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.{{sfn|Potter|2005|p=293}}  Many cities east of the Tigris came under Roman control, including [[Tigranocerta|Tigranokert]], [[Siirt|Saird]], [[Silvan, Diyarbakır|Martyropolis]], [[Bitlis|Balalesa]], [[Bakhchisaray|Moxos]], [[Duhok, Iraq|Daudia]], and Arzan&nbsp;– though under what status is unclear.{{sfn|Millar|1993|p=178}} At the conclusion of the peace, Tiridates regained both his throne and the entirety of his ancestral claim.{{sfn|Barnes|1981|p=18}} 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.{{sfn|Potter|2005|p=293}} 

To strengthen the defence of the east Diocletian had a fortified road constructed at the southern border, where the empire bordered the Arabs, in the year 300. This road would remain in use for centuries but proved ineffective in defending the border as conventional armies could not operate in the region.<ref name="RR">{{Cite book|title=Rome Resurgent: War and Empire in the Age of Justinian|last=Heather, P. J. (Peter J.)|isbn=978-0-19-936274-5|location=New York |publisher=Oxford University Press |oclc=1007044617|year = 2018}}</ref>