Constantine I, byname Constantine the Great, Latin in full Flavius Valerius Constantinus (born February 27, after ad 280?, Naissus, Moesia [now Niš, Serbia]—died May 22, 337, Ancyrona, near Nicomedia, Bithynia [now İzmit, Turkey]), the first Roman emperor to profess Christianity. He not only initiated the evolution of the empire into a Christian state but also provided the impulse for a distinctively Christian culture that prepared the way for the growth of Byzantine and Western medieval culture.
Constantine was born probably in the later ad 280s. A typical product of the military governing class of the later 3rd century, he was the son of Flavius Valerius Constantius, an army officer, and his wife (or concubine) Helena. In ad 293 his father was raised to the rank of Caesar, or deputy emperor (as Constantius I Chlorus), and was sent to serve under Augustus (emperor) Maximian in the West. In 289 Constantius had separated from Helena in order to marry a stepdaughter of Maximian, and Constantine was brought up in the Eastern Empire at the court of the senior emperor Diocletian at Nicomedia (modern İzmit, Turkey). Constantine was seen as a youth by his future panegyrist, Eusebius, bishop of Caesarea, passing with Diocletian through Palestine on the way to a war in Egypt.