This prince, afterward Constantine the Great, was the son of Constantius and Helena, who was said to have been the daughter of an inn-keeper. When Constantius became Cæsar he divorced Helena, and her son was, in a measure, neglected. Constantine, however, soon distinguished himself as a soldier, and won the affection of the army. In appearance he was tall, dignified, and pleasing; he excelled in all military exercises, was modest, prudent, and well informed. He soon attracted the jealousy of Galerius, who would have put him to death had he not escaped to his father in Britain; and now Galerius refused to allow him any higher title than that of Cæsar.
Maxentius, the son of the abdicated emperor Maximian, was also proclaimed Augustus by his soldiers, and prevailed upon his father once more to ascend the throne. Severus, who marched against them, was defeated and put to death; and Constantine now married Fausta, the daughter of Maximian. Galerius led a large army from the East, but was repulsed from Rome and retreated, leaving Maximian and his son masters of the capital. Galerius next associated Licinius with him in his power, and there were now six sovereigns upon the throne.
In A.D. 310, however, Maximian, having conspired against the life of Constantine, was put to death; Galerius died the next year; in A.D. 312 Maxentius fell before the arms of Constantine, and was drowned in the Tiber while attempting to make his escape. It was during this campaign that Constantine is said to have seen the miraculous cross in the heavens.
The Roman Senate paid unusual honors to Constantine; games and festivals were instituted in memory of his victory over Maxentius, and a triumphal arch was erected, whose imperfect architecture shows the decline of ancient taste. The Arch of Trajan was stripped of its ornaments to adorn that of Constantine.
The new emperor introduced good order into the administration of the West, revived the authority of the Senate, and disbanded the Prætorian Guards; he revoked the edicts against the Christians, and paid unusual deference to the bishops and saints of the Church. The Emperor Licinius, who had married his sister, in A.D. 313 defeated and put to death Maximin, so that the empire was now shared between Constantine and Licinius.
The former now summoned a council of bishops at Arles to suppress the heresy of the Donatists, but, before it met, was forced to march against Licinius, who had conspired against him. Licinius was defeated in two battles, and forced to give up a large part of his dominions to his conqueror. Constantine next defeated the Goths and Sarmatæ. Licinius had assumed the defense of Paganism, while Constantine raised the standard of the Cross. The last struggle between them took place near Adrianople; the Pagan army was defeated and put to flight, and in A.D. 324 Licinius was put to death. Thus Constantine reigned alone over the empire of Augustus.
At the famous Council of Nice, which met in A.D. 325, the doctrine of the Trinity was established, Arianism condemned, and at the same time the emperor was, in effect, acknowledged to be the spiritual head of the Church. But an event now occurred which must have destroyed forever the happiness of Constantine. He was induced to put to death his virtuous son Crispus, through the false accusations of his wife Fausta, and when afterward he discovered the falseness of the charges made against Crispus, he directed Fausta and her accomplices to be slain.
Rome, which had so long been the capital of the world, was now to descend from that proud position and become a provincial city. When Constantine returned to Rome after the Council of Nice, he found himself assailed with insults and execrations. The Senate and the people of the capital saw with horror the destroyer of their national faith, and they looked upon Constantine as accursed by the gods. The execution of his wife and son soon after increased the ill feeling against the emperor, and Constantine probably resolved to abandon a city upon which he had bestowed so many favors, and which had repaid him with such ingratitude. He was conscious, too, that Rome, seated in the heart of Italy, was no longer a convenient capital for his empire, and he therefore resolved to build a new city on the site of ancient Byzantium. The Bosphorus, a narrow strait, connects the Black Sea and the Sea of Marmora; and here, on a triangular piece of ground, inclosing on one side an excellent harbor, Constantine laid the foundations of his capital. It was situated in the forty-first degree of latitude, possessed a temperate climate, and a fertile territory around it; while, being placed on the confines of both Europe and Asia, it commanded the two divisions of the empire.