Constantinian shift

Constantinian shift is a term used by nontrinitarian Christians, as well as Anabaptist and Post-Christendom theologians, to describe the political and theological aspects of the 4th-century process of Constantine's integration of the imperial government with the church. The term was popularized by the Mennonite theologian John H. Yoder.

The claim that there ever was Constantinian shift has been disputed; Peter Leithart argues that there was a "brief, ambiguous 'Constantinian moment' in the fourth century," but that there was "no permanent, epochal 'Constantinian shift'."

Constantine I (reigned 306–37) adopted Christianity as his system of belief after the Battle of Milvian Bridge in 312. His victorious legions fought under the "labarum", a standard with the first two Greek letters of Christ's name (XP).

In 313 the Edict of Milan legalised Christianity alongside other religions allowed in the Roman Empire. In 325 the First Council of Nicaea signalled consolidation of Christianity under an orthodoxy endorsed by Constantine, and though this did not make other Christian groups outside the adopted definition illegal, the dissenting Arian bishops were initially exiled. But Constantine reinstated Arius just before the heresiarch died in 336 and exiled the Orthodox Athanasius of Alexandria from 335 to 337. In 380 Emperor Theodosius I made Christianity the Roman Empire's official religion (see State church of the Roman Empire, Byzantine Empire and the Goths) and did enforce the edict. In 392 Theodosius passed legislation prohibiting all pagan cultic worship.

...
Wikipedia