Diocletian

A soldier of obscure provincial origin, Diocletian rose through the ranks of the Roman army to end the half-century of crisis that had nearly destroyed the empire. He was born around AD 244 in Dalmatia, probably near Salona, of humble family. Serving under the emperors of the 270s and 280s, he commanded the household cavalry under Numerian, and when that emperor died in suspicious circumstances in 284 the army in the east proclaimed Diocletian emperor. He killed the praetorian prefect Aper, whom he blamed for Numerian's death, and in 285 defeated Numerian's brother Carinus to become sole ruler.

Convinced that the empire was too large for one man to defend, he divided its government. In 286 he raised his comrade Maximian to co-emperor in the west, and in 293 he completed the system known as the Tetrarchy, appointing Galerius and Constantius Chlorus as junior emperors (Caesars) under the two senior Augusti. The arrangement was cemented by marriage alliances: Galerius married Diocletian's daughter Valeria, and Constantius married Maximian's stepdaughter Theodora. The four rulers campaigned continuously, defeating Persia, suppressing revolts in Egypt and Britain, and restoring the frontiers.

Diocletian reorganized the empire's administration, roughly doubling the number of provinces and grouping them into dioceses under a new layer of officials, separating civil from military command. He reformed taxation and the coinage, and in 301 issued the Edict on Maximum Prices, an ultimately unsuccessful attempt to fix prices and wages throughout the empire. Court ceremony was elaborated on quasi-Persian lines, the emperor now approached with prostration and addressed as dominus. In 303, urged on by Galerius, he began the Great Persecution, the most systematic attempt to suppress Christianity in Roman history, with churches demolished, scriptures burned, and clergy and laity imprisoned or executed.

In 305, weakened by illness, Diocletian abdicated at Nicomedia and compelled Maximian to do the same — the first Roman emperor to resign the office voluntarily. He retired to a fortified palace at Split on the Dalmatian coast, around which the modern city later grew, reportedly declining appeals to return to power by praising the cabbages he grew there. He died in 311, as the tetrarchic system he had built dissolved in the civil wars from which Constantine emerged.