Tetrarchy

The Tetrarchy was the system instituted by <a href="/facts/Roman_emperor/sT4nFc67">Roman emperor</a> <a href="/facts/Diocletian/l4Inf5wa">Diocletian</a> in 293 AD to govern the ancient Roman Empire by dividing it between two emperors, the <a href="/facts/Augusti/1mHIqsde">augusti</a>, and their junior colleagues and designated successors, the <a href="/facts/Caesares/75YBKUXu">caesares</a>. 
Initially Diocletian chose <a href="/facts/Maximian/Bfhf6oCY">Maximian</a> as his caesar in 285, raising him to co-augustus the following year; Maximian was to govern the western provinces and Diocletian would administer the eastern ones. The role of the augustus was likened to <a href="/facts/Jupiter_(mythology)/JPetM2m9">Jupiter</a>, while his caesar was akin to Jupiter's son <a href="/facts/Hercules/a0GTSxvm">Hercules</a>. <a href="/facts/Galerius/gCyV36Ij">Galerius</a> and <a href="/facts/Constantius_Chlorus/YX5SFTF2">Constantius</a> were appointed caesares in March 293. Diocletian and Maximian retired on 1 May 305, raising Galerius and Constantius to the rank of augustus. Their places as caesares were in turn taken by <a href="/facts/Valerius_Severus/yLfCsQhH">Valerius Severus</a> and <a href="/facts/Maximinus_Daza/SHkNXQnA">Maximinus Daza</a>.
The orderly system of two senior and two junior rulers endured until Constantius died in July 306, and his son <a href="/facts/Constantine_the_Great/jW1q8TPp">Constantine</a> was unilaterally acclaimed augustus and caesar by his father's army. Maximian's son <a href="/facts/Maxentius/BG0hzPLG">Maxentius</a> contested Severus' title, styled himself princeps invictus, and was appointed caesar by his retired father in 306. Severus surrendered to Maximian and Maxentius in 307. Maxentius and Constantine were both recognized as augusti by Maximian that same year. Galerius appointed <a href="/facts/Licinius/726hJYdG">Licinius</a> augustus for the west in 308 and elevated Maximinus Daza to augustus in 310.
Constantine's victory over Maxentius at the <a href="/facts/Battle_of_the_Milvian_Bridge/pNcYBGlL">Battle of the Milvian Bridge</a> in 312 left him in control of the western part of the empire, while Licinius was left in control of the east on the death of Maximinus Daza. Constantine and Licinius jointly recognized their sons – <a href="/facts/Crispus/VAbFIzuX">Crispus</a>, <a href="/facts/Constantine_II_(emperor)/FwUu1CSS">Constantine II</a>, and <a href="/facts/Licinius_II/Bqmhmp3W">Licinius II</a> – as caesares in March 317. Ultimately the tetrarchic system lasted until c. 324, when mutually destructive civil wars eliminated most of the claimants to power: <a href="/facts/Licinius/726hJYdG">Licinius</a> resigned as augustus after losing the <a href="/facts/Battle_of_Chrysopolis/r1tTJsoW">Battle of Chrysopolis</a>, leaving Constantine in control of the entire empire.
The <a href="/facts/Constantinian_dynasty/4ACsrp6W">Constantinian dynasty</a>'s emperors retained some aspects of collegiate rule; Constantine appointed his son <a href="/facts/Constantius_II/jKXch2Wa">Constantius II</a> as another caesar in 324, followed by <a href="/facts/Constans/Q1GzfjqH">Constans</a> in 333 and his nephew <a href="/facts/Dalmatius/J0S943rD">Dalmatius</a> in 335, and the three surviving sons of Constantine in 337 were declared joint augusti together, while the concept of the division of the empire under multiple joint emperors endured until the <a href="/facts/Fall_of_the_Western_Roman_Empire/EjUtGSJm">Fall of the Western Roman Empire</a>. In the <a href="/facts/Eastern_Roman_Empire/njEELXWF">Eastern Roman Empire</a>, augusti and caesares continued to be appointed sporadically.

Tetrarchy open-in-new

Tetrarchy