國教
A milestone in the rise of Christianity was the conversion of Emperor Constantine the Great (r. 306–337) in 312, as claimed by his Christian panegyrist Eusebius of Caesarea, although the sincerity of his conversion is debated. Constantine confirmed the legalization of the religion through the so-called Edict of Milan in 313, jointly issued with his rival in the East, Licinius (r. 308–324). By the late 4th century, Emperor Theodosius the Great had made Christianity the State religion, thereby transforming the Classical Roman world, which Peter Brown characterized as "rustling with the presence of many divine spirits."