The Edict of Thessalonica, also known as the Cunctos Populos, was issued on February 27, 380 AD by the Roman Emperors Theodosius I, Gratian, and Valentinian II. This edict is significant in the history of Christianity and the Roman Empire because it marked the formal declaration of Nicene Christianity as the state religion of the Roman Empire, thereby establishing religious conformity within the empire.
The Edict of Thessalonica was issued at a time when the Roman Empire was grappling with religious diversity and the political implications of religious unity. After the Edict of Milan in 313 AD, which granted religious tolerance to Christians, various forms of Christianity had proliferated. The empire saw a rise in different Christian sects, including Arianism, which posed a threat to the unity of the empire through theological disputes. By 380 AD, the emperors sought to consolidate power by promoting a unified religious doctrine:
The Edict of Thessalonica explicitly stated:
"... the Catholic faith that we confess, which is that of Peter of Alexandria, Athanasius of Alexandria, and the Roman Pontiff, Damasus, we will believe this faith, we will observe it, we will order others to observe it..."
The edict:
The immediate impact of the edict was: