page_title: Diocletian
section_title: Foundation of the Tetrarchy
hierarchical_section_title: Diocletian / Tetrarchy / Foundation of the Tetrarchy
caption_attribution_description: English: Arch of Diocletian or Triumphal Arch of the Tetrarchy, Sbeitla, Tunisia Français&#160;: Arc de Dioclétien ou l'arc de triomphe de la tétrarchie, Sbeïtla, Tunisie
context_page_description: Diocletian was a Roman emperor from 284 to 305. Born to a family of low status in Dalmatia, Diocletian rose through the ranks of the military to become a cavalry commander of the Emperor Carus's army. After the deaths of Carus and his son Numerian on campaign in Persia, Diocletian was proclaimed emperor. The title was also claimed by Carus's surviving son, Carinus, but Diocletian defeated him in the Battle of the Margus.
  Diocletian's reign stabilized the empire and marks the end of the Crisis of the Third Century. He appointed fellow officer Maximian as Augustus, co-emperor, in 286. Diocletian reigned in the Eastern Empire, and Maximian reigned in the Western Empire. Diocletian delegated further on 1 March 293, appointing Galerius and Constantius as Caesars, junior co-emperors, under himself and Maximian respectively. Under this 'tetrarchy', or "rule of four", each emperor would rule over a quarter-division of the empire. Diocletian secured the empire's borders and purged it of all threats to his power. He defeated the Sarmatians and Carpi during several campaigns between 285 and 299, the Alamanni in 288, and usurpers in Egypt between 297 and 298.
context_section_description: Some time after his return, and before 293, Diocletian transferred command of the war against Carausius from Maximian to Flavius Constantius, 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, Theodora. On 1 March 293 at Milan, Maximian gave Constantius the office of caesar. In the spring of 293, in either Philippopolis (Plovdiv, Bulgaria) or Sirmium, Diocletian would do the same for Galerius, husband to Diocletian's daughter Valeria, and perhaps Diocletian's Praetorian Prefect. Constantius was assigned Gaul and Britain. Galerius was initially assigned Syria, Palestine, Egypt, and responsibility for the eastern borderlands.
  This arrangement is called the tetrarchy, from a Greek term meaning "rulership by four". The Tetrarchic Emperors were more or less sovereign in their own lands, and they travelled with their own imperial courts, administrators, secretaries, and armies. 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 the departure of Diocletian and Maximian. Maximian's son Maxentius and Constantius's son Constantine would then become Caesars. In preparation for their future roles, Constantine and Maxentius were taken to Diocletian's court in Nicomedia.
caption: Triumphal arch of the tetrarchy, Sbeitla, Tunisia
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