The first section addresses the debate between Julian’s supporters and detractors following his sudden death in 363. Christian preachers turned Julian’s propagandistic use of his life into proof that Roman history was regulated by Christian providence. However, they also had to confront Julian’s re-assessment of the power dynamics between the ruler and the priests in the post-Constantinian empire. I argue that Julian was wary of how the identification of religious allegiance as the criterion for determining whether an emperor was a philosopher-ruler affected the interaction between the emperor, now decentred from his religious structures of choice, and the ecclesiastical leaders. The second section shows that that the episcopal engagement with philosophical ideas both provided clerics with a weapon against Julian’s attempts to re-centre the ruler in religious matters and shaped the relationship between the bishops and emperors in addressing heresy - a key challenge faced by Christianity in its self-construction as perfect system of knowledge. Episcopal appeals to an exclusive control of knowledge also affected the public role of non-conforming philosophers, which I illustrate with a case study of Synesius of Cyrene.