The authority of the Roman emperors in the religious affairs of the Roman Empire stemmed from the adoption of the old republican office of pontifex maximus by the first Roman emperor, Augustus. This role gave the emperors not only formal responsibility for maintaining the traditional cults, but also broad ideological legitimacy as guardians of the spiritual order of the state. Their influence lasted throughout the entire existence of the Roman Empire and continued in the Eastern Roman Empire, where it gradually intertwined with Christian imperial ideology. The emperors regularly intervened in the internal matters of all cults within the empire and, after the triumph of Christianity, also shaped church doctrine by convening and directing major ecumenical councils.
Stanislav Doležal (Tue,) studied this question.