DIOCLETIAN (GAIUS AURELIUS VALERIUS DIOCLETIANUS) (A.D. 245-313), Roman emperor 284-305, is said to have been born at Dioclea, near Salona, in Dalmatia. His original name was Diocles. Of humble origin, he held important military com mands under the emperors Probus and Aurelian, and accom panied Carus to the Persian War. After the death of Numerianus he was chosen emperor by the troops at Chalcedon, on Sept. 17, 284, and slew with his own hands Arrius Aper, the praefect of the praetorians. Having been installed at Nicomedia, he received general acknowledgment after the murder of Carinus. In con sequence of the rising of the Bagaudae in Gaul, and the threaten ing attitude of the German peoples on the Rhine, he appointed Maximian Augustus in 286; and, in view of further dangers and disturbances in the empire, proclaimed Constantius Chlorus and Galerius Caesars in 293. Each of the four rulers was placed at a separate capital—Nicomedia, Mediolanum (Milan), Augusta Tre virorum (Trier), Sirmium. This amounted to an entirely new organization of the empire, on a plan commensurate with the work of government which it now had to carry on. Diocletian abdicated his sovereignty on May 1, 305, and retired to Salona, where he died eight years afterwards (others give 316 as the year of his death). The end of his reign was memorable for the perse cution of the Christians. He hoped to strengthen the empire by reviving the old religion, and the church as an independent State appeared to be a standing menace to his authority.
Under Diocletian the senate became a political nonentity, the last traces of republican institutions disappeared, and were re placed by an absolute monarchy. He wore the royal diadem, as sumed the title of lord, and introduced the whole ceremonial of Eastern monarchy. His first work was the reform of the adminis tration of the empire ; this is partly dealt with under ROME : His tory, and a brief summary is all that can be attempted here. The titular supremacy of Italy disappears, and a uniform system of administration comes into play throughout the empire. Beginning with Diocletian, local autonomy gradually disappears, and the em pire is administered by a huge bureaucracy, entirely dependent on the emperor. The empire was sick of civil war and continual insecurity, and Diocletian and his successors saved it at the price of practically destroying its economic and political life. The old, regular, intricate system of taxation was abolished, and a simpli fied, but oppressive and inelastic system substituted, which was really a systematization of the practice of exacting forced contri butions of produce and labour, based on acreage, which resulted in the country people becoming compulsorily tied to their land. The responsibility for the city taxes was put on the members of the municipal councils. In the military sphere Diocletian only laid the foundations of the new system, which was the work of Constantine, but he took the first steps by largely increasing the numbers of the army. His attempted stabilization of prices (see DIOCLETIAN, EDICT OF) was a failure. In addition, he adorned the city with numerous buildings, such as the thermae, of which extensive remains are still standing (see AURELIUS VICTOR, de Caesaribus 39; Eutropius ix. 13; Zonaras xii., 31) . The problem before Diocletian was much the same as that before Augustus but the conditions were much more unfavourable. "By his genius Augustus succeeded in restoring not only the State but also the prosperity of the people. Diocletian and Constantine sacrificed the interests of the people to the preservation of the State." See M. Rostovtzev, Social and Economic History of the Roman Empire (1926) ; and ROME, History.