Constantine I, Roman emperor or Constantine the Great (kn´stntn, –tn) (KEY) , 288?–337, Roman emperor, b. Naissus (present-day Ni, Yugoslavia). He was the son of Constantius I and Helena and was named in full Flavius Valerius Constantinus.

Rise to Power
When his father was made caesar (subemperor), Constantine was left at the court of the emperor Diocletian, where he was under the watchful eye of Galerius, who was caesar with Constantius. When Diocletian and Maximian resigned in 305, Constantius and Galerius became emperors.

Constantius requested that Constantine be sent to him in Britain, and Galerius reluctantly complied. Constantius died at York the next year. There, his soldiers proclaimed Constantine emperor, but much rivalry for the vacated office ensued. In Italy, Maxentius, supported by the Romans and by his father Maximian, vied with Severus and Galerius. Constantine, accepting the lesser title of caesar from Galerius, remained aloof while Maxentius and Maximian defeated Severus and Galerius.

Constantine made an alliance with Maximian, marrying his daughter Fausta and recognizing Maxentius after a fashion. When Maximian, in dispute with his son, fled to Constantine, Constantine received and sheltered him until Maximian, in an attempt to regain the throne, undertook (310) a revolt against Constantine’s rule in Gaul. Unsuccessful against Constantine, Maximian was forced to commit suicide.

Constantine, having already declared against Maxentius and ignoring the fact that Galerius had recognized Licinius in the East, now considered himself emperor. When Galerius died in 310, still another claimant to the imperial throne appeared in Maximin (d. 313), who allied himself with Maxentius against the alliance of Licinius and Constantine. While Licinius attacked Maximin, Constantine moved into Italy against Maxentius. The rivals for Italy met (312) at the Milvian or Mulvian Bridge over the Tiber near Rome. Before the battle Constantine, who was already sympathetic toward Christianity, is said by Eusebius of Caesarea to have seen in the sky a flaming cross inscribed with the words, "In this sign thou shalt conquer." He adopted the cross and was victorious. Maxentius was routed and killed. The battle is regarded as a turning point for Christianity.

In 313 Constantine and his fellow emperor, Licinius, met at Milan and there issued the so-called Edict of Milan, confirming Galerius’ edict of 309, which stated that Christianity would be tolerated throughout the empire. The edict in effect made Christianity a lawful religion, although it did not, as is sometimes believed, make Christianity the official state religion.

No longer having Maximin to contend with, Licinius challenged Constantine, and a brief struggle followed. Constantine, victorious, took (315) control over Greece and the Balkans, and the uneasy peace that followed lasted until 324, when Licinius again vied with Constantine. This time Licinius lost his throne and ultimately his life.

A Christian Empire
Constantine was now sole ruler of the empire, and in a reign of peace he set about rebuilding the strength of old Rome. Constantine continued to tolerate paganism and even to encourage the imperial cult. At the same time, however, he endeavored to unify and strengthen Christianity.

In 314 he convened a synod at Arles to regulate the Church in the West, and in 325 he convened and presided over a council at Nicaea to deal with the troubles over Arianism (see Nicaea, First Council of). Thus Constantine evolved the idea of the ecumenical council. In 330 he moved the capital to Byzantium, which was rebuilt as Constantinople, a city predominantly Christian and dedicated to the Virgin. He seems to have favored compromise with Arianism, and in 335, in defiance of the Council of Tyre, he exiled St. Athanasius.

As the founder of the Christian empire, Constantine began a new era. He was an absolute ruler, and his reign saw the culmination of the tendency toward despotic rule, centralized bureaucracy, and separation of military and civil powers evolved by Diocletian. Constantine’s legal reforms were marked by great humanity, perhaps a result of Christian influence. Though he had done much to unify the empire, at his death Constantine divided it again, providing for his three surviving sons and also to some extent for the sons of his half brother. These nephews were soon killed (though others, notably Julian the Apostate, survived), but complex contests ensued between Constans I, Constantine II, and Constantius II.

Historians differ greatly in their assessments of Constantine’s motives and the depth of his Christian conviction. Early Christian writers portray him as a devout convert, although they have difficulty explaining his execution in 320 (on adultery charges) of Crispus, his son by his first wife, and Fausta, his wife. Some later historians see him as a political genius, expediently using Christianity to unify his empire. An intermediate interpretation pictures him as a pagan gradually converted to Christianity (he was baptized on his deathbed), using his new belief for personal ends much as earlier emperors had used the imperial cult.

Bibliography
The chief contemporary historians of Constantine’s reign are Lactantius and Eusebius. See also biographies by N. H. Baynes (1931, repr. 1972), L. B. Holsapple (1942), A. H. M. Jones (rev. ed. 1962), J. H. Smith (1971), and F. G. Slaughter (1972); C. B. Coleman, Constantine the Great and Christianity (1914); G. P. Baker, Constantine the Great and the Christian Revolution (1930, repr. 1967).

The Columbia Encyclopedia, Sixth Edition. Copyright © 2001 Columbia University Press.