It has become an axiom of historical research that the decline of the western Empire in the second half of the thirteenth century led to a concomitant decline in subscription to the idea that a ruler might exercise temporal authority beyond the bounds of his kingdom. An increase in the authority exercised by rulers of the western kingdoms and the rediscovery of Aristotelian learning led to a new conception of autonomous states. This thesis tests the validity of this assessment by determining the place occupied by the Empire in French thought. It establishes the factors which formulated perceptions of contemporary rulers of the medieval Empire between Frederick II’s accession and the outbreak of the Hundred Years War. It examines the place occupied in French thought by the figure most widely associated with the Empire in France, the Carolingian emperor Charlemagne. It determines French conceptions of the nature of the Empire as an institution, the role that it and its ruler were considered to occupy in the world, and their relationship with the French kingdom. Rather than base its examination upon the small number of texts traditionally associated by historians with the development of a new political ideology, a broader context is established by using the widest possible source base. The consequence is a portrait of the place occupied by the Empire and its ruler in French thought that differs profoundly from the widely accepted historical model. On one level the Empire and its ruler were considered to differ very little from the French kingdom. Yet, far from abandoning the concept of universal temporal authority, the inhabitants of France also considered the emperor to fulfil a supra-regnal role necessary in a properly ordered Christian society and increasingly conceived of in terms of the leadership of the crusade.