It is almost a commonplace that the ideology and circumstances of the Carolingian empire made possible assertion by the Frankish episcopacy of an increasingly active role in the government of ninth-century Frankish Europe. Restoration of the ecclesiastical hierarchy begun in the mid-eighth century by Pepin the Short and completed under his son, the emperor Charles, resulted in the establishment of a class of able men whose common interests were closely bound up with preservation and extension of the imperial structure; in the reign of Charles' successors this group came to be involved more and more prominently in the workings of the empire, as events in the forty years following Charles' death necessitated rapid reinterpretation of that entity. In that process no member of the hierarchy played a more ubiquitous part than did Ebbo, archbishop of Reims from 816 until his deposition nineteen years later. Loyal to the principles of imperial rule while at the same time betrayer of the friendship and fealty owed his monarch, Ebbo was scholar, builder, missionary, high public official, rebel and outcast during a career inextricably bound up with the course and transmutations of the empire. In the range of his activities and influence almost a paradigm of those opportunities and tasks open to the Carolingian episcopate, his history is in no small measure that of the empire itself and of the church with which in the ninth century that empire was conceived to be coextensive, even identical. It is those two histories and their interrelations that form the subject of the present paper.