On the eve of his battle against Maxentius at Milvian Bridge in 312, Flavius Valerius Constantinus (ca. 273/74–337) reportedly saw a symbol in the sky, which played a role in his conversion to faith in the Christian God and began a new chapter in the relationship between church and state. What happens to the church when the emperor becomes a Christian? Should such a triumph be perceived as God’s will and the fulfilment of prophecy? Or, was it the beginning of compromise and worldly captivity for a pilgrim people? Constantine’s life—his career, faith, and relationship to the church—raises questions for Christians and for historians of the church which cannot be ignored. The aim of the present work is to reassess our picture of Constantine through careful historical inquiry largely within the scope of the early Christian period. Our approach is threefold: to re-examine the history surrounding Constantine’s life, to consider his connection to the development of Christian theology, and to then assess his legacy regarding the church.