Edict of Thessalonica

The Edict of Thessalonica (also known as Cunctos populos), issued on 27 February 380 AD by three reigning Roman Emperors, ordered all subjects of the Roman Empire to profess the faith of the bishops of Rome and of Alexandria, making Nicene Christianity the state religion of the Roman Empire.

In 313 the emperor Constantine I, together with his eastern counterpart Licinius, issued the Edict of Milan, which granted religious toleration and freedom for persecuted Christians. By 325 Arianism, a school of christology which contended that Christ the Word did not possess the divine essence of the Father but was rather a primordial creation and an entity subordinate to God, had become so sufficiently widespread and controversial in Early Christianity that Constantine called the Council of Nicaea in an attempt to end the controversy by establishing an empire-wide, i.e., "ecumenical" orthodoxy. The council produced the original text of the Nicene Creed, which rejected the Arian confession and upheld that Christ is "true God" and "of one essence with the Father."

However, the strife within the Church did not end with Nicaea, and the Nicene creedal formulation remained contentious even among anti-Arian churchmen. Constantine, while urging tolerance, began to think that he had come down on the wrong side, and that the Nicenes — with their fervid, reciprocal persecution of Arians — were actually perpetuating strife within the Church. Constantine was not baptized until he was near death (337), choosing a bishop moderately sympathetic to Arius, Eusebius of Nicomedia, to perform the baptism.

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