Constantine I., Roman emperor, 306-337 A.D. FLAVIUS VALERIUS AURELIUS CONSTANTINUS, surnamed 'the Great,' was born in 274, at Naissns, in Upper Mœsia. He was the eldest son of Constantius Chlorus and Helena, and first distinguished himself as a soldier in Diocletian's famous Egyptian expedition (296), next under Galerius in the Persian war. In 305, the two emperors, Diocletian and Maximian, abdicated, and were succeeded in the supreme rank of Augustus by the two Cæsars, Constantius Chlorus and Galerius. Galerius, envious of young Constantine's brilliant genius and popularity among the soldiers, took every means of exposing him to danger, and it was now that he acquired that mixture of reserve, cunning, and wisdom which was so conspicuous in his conduct in after-years. At last, extorting a reluctant consent from the jealous Galerius, he made his way hastily to his father, who ruled in the West, and joined him at Boulogne just as he was setting out on an expedition against the Picts in North Britain (306). Constantius died at York in the same year, having proclaimed his son Constantine his successor. The latter now wrote a conciliatory letter to Galerius, and requested to be acknowledged as Augustus. Galerius did not dare to quarrel with Constantine, yet he granted him the title of Cæsar only. Political complications now increased, until in 308 there were actually no less than six emperors at once—Galerius, Licinius, and Maximin in the East; and Maximian, Maxentius his son, and Constantine in the West. Maxentius having quarrelled with his father, forced him to flee from Rome; he took refuge with Constantine, who had married his daughter Fausta at Arles in 307, but was ungrateful enough to plot the destruction of his benefactor. This being discovered, he fled to Marseilles, the inhabitants of which were just about to give him up to the conqueror, when he anticipated his fate by suicide (309). Maxentius professed great anger at the death of his father, and assembled a large army, with which he threatened Gaul. Constantine anticipated his movements by crossing the Alps by Mont Cenis, and invading Italy. Already twice he had defeated Maxentius, when he finally crushed his power by the great victory of the Milvian Bridge, near Rome, 28th October 312. Maxentius himself was pressed by the thronging crowd of fugitives over the bridge into the river, and drowned. Constantine now entered the capital, disbanded the Prætorian guards, and destroyed their camp. During his short stay in Rome he assumed the title of Pontifex Maximus. It was during his final struggle with Maxentius that the famous incident occurred that is said to have caused Constantine's conversion, and which Eusebius gives us an account of from the lips of the emperor himself. At noon there appeared in the sky a flaming cross inscribed Ἐν τοῖτῷ νικά ('By this, conquer'). Again, the night before the final battle, a vision appeared to Constantine in his sleep, bidding him inscribe the shields of his soldiers with the sacred monogram of the name of Christ. Hence the well-known labarum or standard of the cross, which Constantine, however, did not give his army, according to Gibbon, till 323. Whatever the story of the conversion be worth, one satisfactory consequence was the edict of Milan (March 313), issued conjointly with Licinius, and giving civil rights and toleration to Christians throughout the empire.
Constantine was now sole emperor of the West. Similarly, by the death of Galerius in 311, and of Maximin in 313, Licinius became sole emperor of the East. In 314 a war broke out between the two rulers, in which Licinius had the worst, and was fain to conclude a peace by the cession of Illyricum, Pannonia, and Greece. Constantine gave Licinius his sister Constantina in marriage, and for the next nine years devoted himself vigorously to the correction of abuses in the administration of the laws, to the strengthening of the frontiers of his empire, and to chastising the barbarians, who learned to fear and respect his power. In 323 he renewed the war with Licinius, whom he defeated, and ultimately put to death. Constantine was now at the summit of his ambition, the sole governor of the Roman world. He chose Byzantium for his capital, and in 330 solemnly inaugurated it as the seat of government, under the name of Constantinople or City of Constantine. In 326 he committed a deed that has thrown a dark shade over his memory. His eldest son (by his first wife), Crispus, a galliant and accomplished prince, who was very popular, he put to death on a charge of treason; and next year his own second wife, Fausta, mother of the three sons amongst whom he divided his empire. In 325 was held the great Council of Nicea, in which he opposed the Arians on political grounds, as the weaker party; but not being theologically interested in the dissensions, refrained from active persecution of them. In 324 Christianity became the state religion, the pagan temples were closed, and sacrifices forbidden. Yet it was only a short time before Constantine's death, which occurred 22d July 337, that he would allow himself to be baptised by the Arian bishop, Eusebius of Nicomedia. The story of his baptism at Rome by Pope Sylvester in 326, and of the so-called Donation of Constantine thereafter, alluded to in Dante's Inferno, and often in the past gravely argued as giving an historical basis for the temporal power of the papacy, may safely be dismissed (see CANON LAW). For other Constantines, see BYZANTINE EMPIRE.