James of Viterbo's De regimine Christiano was produced at the height of the great conflict of 1296-1303 between Pope Boniface VIII and Philip the Fair of France. Echoing and elaborating Boniface's Bull Unam sanctam, the treatise is a detailed and rigorous defence of the 'hierocratic' ideology of the thirteenth-century papacy in its most ambitious form. As such, it stands alongside the better-known De ecclesiastica potestate of Giles of Rome, by which it is to some extent influenced. De regimine Christiano is here presented in a new and complete critical edition,...