During the Principate, the negotiation of the ruler’s intellectual authority emerged as a key strategy of political self-legitimisation. In the early fourth century, the definition of early Christian thinking as the perfect system of knowledge, which had been developed through dialogue and rivalry with the post-Hellenistic philosophical schools, encouraged the emperor Constantine to mobilise his allegiance to Christianity for competitive self-assertion: he upheld his conversion as an intellectual achievement with no imperial precedent. Modern reluctance to take ancient definitions of Christianity as philosophy at face value has obscured the force of this propagandistic argument. Yet its recovery is essential to understanding Julian’s philosophical response to the positioning of early Christianity as an authoritative system of knowledge and appreciating the strategies of self-legitimisation pursued by fourth-century bishops in conversation with the (Christian) philosopher-ruler. As the question of who holds authoritative knowledge was antagonised by religious disputes, the fourth-century socio-political and ideological transition was channelled into a ‘politics of interpretation’ in which leaders (imperial and episcopal) negotiated their status as intelligent decoders of providential signs scattered throughout literature, history, and the cosmos.