edict · 380 · Thessalonica
On 27 February 380 Theodosius, with Gratian and Valentinian II, decreed that all peoples of the empire should hold the faith of Peter as taught by Damasus of Rome and Peter of Alexandria — Nicene Christianity became the religion of the Roman state, and the word 'Catholic Christians' entered law.
Theodosius binding the empire to the Nicene faith against Arian remnants.
Nicene Christianity the religion of the Roman people; 'Catholic Christians' defined in law by communion with Rome and Alexandria.