A systematic historical analysis traces the gradual conversion of the Roman emperor and the legitimate establishment and constitution of the Christian Church, weighing competing ancient testimonies and the cautious, often politicized steps by which imperial favor shifted away from pagan cults. The narrative examines administrative measures that restored church property, granted legal immunities, and instituted religious toleration, considers the mixed motives behind edicts and public gestures, and assesses how imperial policy, popular belief, and ecclesiastical organization interacted to reshape institutions and public life across the late empire.