DIOCLETIAN. Valerius Diocletianus (245-313), Roman emperor, was born of obscure parents near Salona, in Dalmatia, and reigned from 284 to 305 a.d. He entered the army and served with high distinction, held important commands under the emperors Probus and Aurelian, and accompanied Carus to the Persian war. After the death of Numerianus he was chosen emperor by the troops at Chalcedon, and slew with his own hands Arrius A per, the prefect of the praetorians. His advent to the throne marks the commencement of the era of Diocletian, August 29, 284. Having been installed at Nicomedia, he received general acknowledgment after the murder of Carinus. He appointed Maximian Augustus in 286, and Constantius Chlorus and Galerius, Caesars in 292. Each of the four rules was placed at a separate capital— Treves, Sirmium, Milan, Nicomedia. This amounted to an entirely new organization of the empire, on a plan commensurate with the work of government which it now had to effect. At the age of fifty-nine, exhausted with labour, he abdicated his sovereignty on May 1, 305, and retired to Salona, the place of his birth, where he died eight years afterwards. His reign was memorable for the persecution of the Christians.