Constantine the Great (c. AD 285–337)

First Christian emperor of Rome and founder of Constantinople. He defeated Maxentius, joint emperor of Rome in AD 312, and in 313 formally recognized Christianity. As sole emperor of the west of the empire, he defeated Licinius, emperor of the east, to become ruler of the Roman world in 324. He presided over the church's first council at Nicaea in 325. Constantine moved his capital to Byzantium on the Bosporus in 330, renaming it Constantinople (now Istanbul).

Constantine was born at Naissus (Niš, Serbia), the son of Constantius. He was already well known as a soldier when his father died in York in 306 and he was acclaimed by the troops there as joint emperor in his father's place. A few years later Maxentius, the joint emperor in Rome (whose sister had married Constantine), challenged his authority and mobilized his armies to invade Gaul. Constantine won a crushing victory outside Rome in 312. During this campaign he was said to have seen a vision of the cross of Jesus superimposed upon the sun, accompanied by the words: ‘In this sign, conquer’. By the Edict of Milan 313 he formally recognized Christianity as one of the religions legally permitted within the Roman empire and in 314 he summoned the bishops of the Western world to the Council of Arles. However, there has never been agreement on whether Constantine adopted Christianity for reasons of faith or as an act of imperial absolutism to further his power. Constantine increased the autocratic power of the emperor, issued legislation to tie the farmers and workers to their crafts in a sort of caste system, and enlisted the support of the Christian church. He summoned, and presided over, the first general council of the church in Nicaea 325. In 337 he set out to defend the Euphrates frontier against the Persians, but he died before reaching it, at Nicomedia in Asia Minor.