After a series of civil wars, Constantine became sole Roman Emperor from 324–37. He converted to Christianity and made Constantinople (Constantinopolis) in the east, named after himself, his imperial residence. He introduced a series of reforms, including the creation of the Prefectura. These were praetorian guards who were the emperor’s chief aides. They were given the responsibility of administering and controlling the four divisions of empire: Gallia, Italia, Illyricum and Oriens. Constantine had witnessed the persecution of the Christians under his predecessor; in 313, under the Edict of Milan, he ended all Christian persecution by legalizing Christianity and supported the church financially. In 325 he summoned the Council of Nicaea, which dealt with the Arian heresy and established the Nicene Creed. There is uncertainty over the exact date of Constantine’s conversion, with some historians arguing that it was on his deathbed in 337.
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