Constantine I the Great (Flavius Valerius Constantinus) (272-337), proclaimed Augustus by his troops in 306; ruled parts of the Empire from 307. Constantine is commonly accepted as one of the greatest Roman Emperors who also helped to shape the course of Western civilization.
He was born at Naissus in Upper Dacia to Constantius 1 Chlorus and an innkeeper's daughter, Helena. Constantine was well educated and served at the court of Diocletian after the appointment of his father as one of the two Caesari, at that time a junior emperor, in the Tetrarchy in 293.
Constantine I rebuilt the ancient Greek city of Byzantium and renamed it Constantinople making it the capital of the empire. He legalized and strongly supported Christianity beginning around the time he became emperor, but he neither made paganism illegal nor made Christianity the state religion. Though the church prospered under Constantine's patronage, it also fell into the first of many public schisms. He himself called the First Council of Nicaea to settle the problem of Arianism, a dispute about the personhood and godhood of Jesus. He himself was not baptized and chrismated until close to his death.