CONSTANTINIANISM is a policy establishing a particular Christian church as the religion of the state, also known as Caesaropapism. Formulated originally by the Roman emperor Constantine I, the Great (d. 337), it was continued in the Byzantine Empire (until 1453), the Frankish kingdom, the Holy Roman Empire (962–1806), and numerous states of Europe, being modified in most states since the Protestant Reformation but persisting in some even today. According to this policy, state and church should form a close alliance so as to achieve mutual objectives.

Constantinianism Conceived

Following his "conversion" in 312, Constantine proceeded by stages to establish Christianity as the sole religion of the empire. From 312 to 320 he tolerated paganism but he elevated the standing of Christianity with increasing vigor. From 320 to 330 he thrust the organization of the church into the foreground and directed a frontal attack on polytheism. From 330 to 337, after moving the capital from Rome to Byzantium, he...