Constantine I (ca. 274-337) was a Roman emperor. He is frequently called "the Great" because of his successes as a general, administrator, and legislator and because of his support of the Christian Church and efforts to maintain Christian unity.

Born Flavius Valerius Constantinus at Naissus (in modern Yugoslavia), Constantine was the son of Constantius Chlorus and his concubine Helena. In 293 his father became the son-in-law and caesar (successor-designate) of Emperor Maximian, who was coruler of the Roman Empire with Emperor Diocletian. In 305 Diocletian and Maximian abdicated, and Chlorus became coruler, having superintendence of the West, while Galerius, Diocletian's son-in-law, superintended the East. The new emperors chose caesars (Maximinus Daia and Falvius Valerius Severus) who were not their relatives. Galerius kept Constantine, who had distinguished himself as a soldier, at his own court, apparently fearing that he might develop imperial ambitions if left with his father. In 306, however, Constantine...