Editing Diocletian (section)

===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}}