In Caesaropapism there are two distinct entities, a secular state and a spiritual church, each with its own defined sphere of authority. The problem arises when the secular ruler, Caesar, asserts authority over the church, acting thus like a pope. Eusebius was a bishop and Agapetus a deacon. Both represented an institution, the Christian church, with an identity akin to that of the Roman senate. The judgment of emperors, the decision as to whether they were to be remembered as heavenly icons or wild beasts, now lay with the clergy. Moreover, Christianity's unique development in the first centuries of its existence had left this institution with a capacity for acting and behaving independently such as senators had not known since the closing days of the republic. The suppression of traditional religions in the new Christian empire is the point at which the church, society and power, intersect.

A striking difference between the porphyry portraits of the senior tetrarchs and the marble head of Constantine, the latter statue's clean-shaven face evokes portraits of Trajan, optimus princeps, and the first emperor, Augustus. The distinction between the porphyry and marble portraits points to another salient aspect of the fourth century, the alternation between periods of religious peace and conflict. Constantine's achievement of sole power as Christian emperor changed everything and nothing. His accession is, indeed, treated as a watershed by those who overlook the rapprochement between Christianity and Platonism in the late third century and who view Diocletian's persecution as the culmination of a sustained anti-Christian policy rather than an aberration. After Constantius' death, Julian moved quickly to put his own imprint on Roman power. Receiving reinforcements from Gratian, Theodosius' first task was to deal militarily with the Visigothic problem. In the East, Theodosius too became increasingly hostile toward traditional cult.