Well, it was in 384 A.D. when Siricius (384-399) became the first Roman Bishop to call himself “Pontifex Maximus” and the first time “POPE” was a title. Constantine “legalized” Christianity with the Edict of Milan in A.D. 313 but one could resonably say it really started as the RCC in A.D. 325 when Constantice called the Council of Nicea in an attempt to unify all the Roman religions. The formal combining of paganism and Christianity was fully embraced at that time and has continued to this day in the RCC.
So you reject the Council of Nicaea as ‘paganism’?