Diocletian

Gaius Aurelius Valerius Diocletianus (c. 22 December 244 – 3 December 311), born Diocles (Διοκλῆς) and commonly known as Diocletian (ˌdаɪ.ɵˈkliːʃən), was Roman Emperor from 20 November 284 to 1 May 305. Born to an Illyrian family of low status, he rose through the ranks of the military to become cavalry commander to the emperor Carus. After the deaths of Carus and his son Numerian on campaign in Persia, Diocletian was acclaimed emperor by the army. A brief confrontation with Carus' other surviving son Carinus at the Battle of the Margus removed the only other claimant to the title. With his ascension to power, he ended the Crisis of the Third Century. Diocletian appointed fellow-officer Maximian his Augustus, his senior co-emperor, in 285. He delegated further on 1 March 293, appointing Galerius and Constantius as Caesars, junior co-emperors. Under this "Tetrarchy", or "rule of four", each emperor would rule over a quarter-division of the empire. In campaigns against Sarmatian and Danubian tribes (285–90), the Alamanni (288), and usurpers in Egypt (297–98), Diocletian secured the empire's borders and purged it of threats to his power. In 299, Diocletian led negotiations with Sassanid Persia, the empire's traditional enemy, and achieved a lasting and favorable peace.