The answer
Emperor Constantine changed the course of the world history. After accepting Christianity, he reconstructed Byzantium, renaming it Constantinople and made Christianity, which until then had suffered blood persecution, the official religion of the State.Constantine built several churches and became involved in ecclesiastical politics, going so far as to convene the first world-wide "ecumenical" council in Church history in Nicea in 325.
Constantine was not baptized until close to his death in 337, by the Arian bishop Eusebius of Nicomedia, who happened to be the bishop of the region at that time despite his being an overt ally of Arius. At the Council of Nicea, Eusabius' defense of Arius had angered the emperor and sent him into exile. Constantine might have chosen Eusebius because he was distantly related to the imperial family, and a close friend of Constantine's sister who secured his recall from exile.
Answered by His Eminence Metropolitan Youssef (opens in a new tab)