Diocletian << `dy` uh KLEE shuhn >> was emperor of Rome from A.D. 284 to 305, when he gave up power. While emperor, he sought to stabilize the Roman Empire, improve its ability to withstand outside threats, and recover territory lost to rebels and invaders.
Gaius Aurelius Valerius Diocletianus was born in Dalmatia (present-day Croatia). He rose from a humble background to command the Roman emperor’s bodyguard. After Emperor Numerianus was assassinated in 284, Diocletian’s soldiers proclaimed him emperor.
To provide more effective rule, and hoping to eliminate rivalry over succession to the throne, Diocletian created a tetrarchy (rule of four) in 293. Two co-emperors known as Augusti, Diocletian and Maximian, led the tetrarchy. Two deputies called Caesars, Galerius and Constantius, ruled under the Augusti.
An active reformer, Diocletian nearly doubled the size of the army and improved its command structure. He developed a new system of taxation and created smaller provinces with more officials to oversee local matters. Diocletian’s image was that of a lofty ruler who favored obedience over individual freedom. He promoted Roman tradition, especially traditional Roman religion. For this reason, he ordered the persecution of Christians beginning in 303.
See also Rome, Ancient (The decline of the empire).