The New International Encyclopædia/Diocletian

​DIOCLETIAN, Gaius Aurelius Valerius Diocletianus. A Roman Emperor (A.D. 284–305). He was born of humble parents in Dalmatia (A.D. 245). He adopted a military career, and served with distinction under Aurelian and Probus, accompanied Carus on his Persian campaign, and finally, on the murder of Numerianus having been discovered at Chalcedon, he was proclaimed Emperor in 284 by the army on its homeward march. The suspected assassin of Numerianus, the prefect Arrius Aper, he slew with his own hands, in order, it is alleged, to fulfill a prophecy communicated to him, while still a lad, by a Druidess of Gaul, that he should accede to a throne as soon as he had killed an aper (wild boar). In 285 Diocletian commenced hostilities against Carinus (the joint Emperor along with the deceased Numerianus), who, although victorious in the decisive battle that ensued, was murdered by his own officers, thus leaving to Diocletian the undisputed supremacy. His first years of government were so molested by the incursions of barbarians that, in order to repel their growing aggressiveness, he took to himself a colleague—namely, Maximian—who, under the title of Augustus, ​became joint Emperor in 286. Diocletian reserved for himself charge of the eastern half of the Empire, and gave the western to Maximian. Still the attacks of the barbarians continued as formidable as ever. The Empire was menaced by the Persians in the east, by the Germans and other barbarians in the west; and in order to provide for its permanent security, Diocletian subjected it to a still further division. In 292 Constantius Chlorus and Galerius were proclaimed as Cæsars, and the distribution of the Roman Empire was now fourfold, Diocletian taking the east, with Nicomedia as his seat of government; Maximian, Italy and Africa, with Milan as his residence; Constantius, Britain, Gaul, and Spain, with Treves as his headquarters; Galerius, Illyricum and the entire valley of the Danube, with Sirmium as his imperial abode. It was upon his colleagues that most of the burden of engaging actively in hostilities fell, as Diocletian seldom took the field in person. Among the conquests, or rather reconquests, that were made under his rule, may be enumerated that of Britain, which, after maintaining independence under Carausius and Allectus, was, in 296, restored to the Empire; that of the Persians, who were defeated and compelled to capitulate in 298; and that of the Marcomanni and others of the northern barbarians, who were driven beyond the Roman frontier. Diocletian, after twenty-one years’ harassing tenure of government, desired to pass the residue of his days in tranquillity. On May 1, 305, accordingly, he abdicated the imperial throne at Nicomedia, and compelled his colleague Maximian (much against the latter’s will) to do likewise at Milan. Diocletian sought retirement in his native province of Dalmatia, and for eight years resided at Salona (now Spalato), devoting himself to philosophic reflection, to rural recreation, and to horticultural pursuits. Two years before his abdication he was instigated by his colleague Galerius to that determined and sanguinary persecution of the Christians for which his reign is chiefly memorable. He died in 313. Consult Mason, The Persecution of Diocletianus (London, 1876).