the reign of the roman emperor diocletian was notable for
Diocletian Diocletian (/ˌdaɪ.əˈkliːʃən/; Latin: Gaius Aurelius Valerius Diocletianus Augustus), born Diocles (22 December 244–3 December 311),[3][5] 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 Roman cavalry commander to the Emperor Carus. After the deaths of Carus and his son Numerian on campaign in Persia, Diocletian was proclaimed emperor. The title was also claimed by Carus' 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. Galerius, aided by Diocletian, campaigned successfully against Sassanid Persia, the empire's traditional enemy. In 299 he sacked their capital, Ctesiphon. Diocletian led the subsequent negotiations and achieved a lasting and favourable peace.
Western Roman Empire Though the Empire had seen periods with more than one Emperor ruling jointly before, the view that it was impossible for a single emperor to govern the entire Empire was established by Emperor Diocletian following the disastrous civil wars and disintegrations of the Crisis of the 3rd century. His ideas were instituted in Roman law by the introduction of the Tetrarchy in AD 286, which divided the position of Augustus (Emperor) into two; one in the East and one in the West, each with an appointed Caesar (junior Emperor and designated successor). Though the tetrarchic system would collapse in a matter of years, the East-West administrative division would endure in one form or another for centuries to come. As such, the Western Roman Empire would exist intermittently in several periods between the 3rd and 5th centuries. Though some emperors, such as Constantine I and Theodosius I, would manage to rise to the position of Augustus in both parts and as such reunify the Empire, it would often divide again upon their deaths. After the death of Theodosius I in AD 395, the Empire was divided between his sons and would not be reunified. Eighty-five years later, in 480, following various invasions and the collapse of central control in the West, Emperor Zeno of the Eastern Empire recognized the reality of the Western Empire's reduced domain. Effective central control had ceased to exist even in the Italian Peninsula after the depositions of Julius Nepos and Romulus Augustulusâ€”and Zeno therefore abolished the Western court and proclaimed himself the sole emperor of the Roman Empire.