This chapter shows that the Carolingian way of dealing with the Adoptionist challenge was to allow a conversation between the Spanish bishops and their Frankish opponents to take place. It also explores some of the ways in which the Carolingians used this controversy to claim for themselves the authority to determine the difference between orthodoxy and heterodoxy. In so doing, the Adoptionist controversy helped them further to consolidate a sense of ecclesiastical unity with the sacrum palatium at its centre out of the many different visions of community within the emerging empire. Among the rulers who could serve as an exemplary arbiter to Charlemagne, Constantine's place in both Spanish and Frankish ecclesiastical history represented the risks and rewards inherent in such an involvement. Both sides in the Adoptionist controversy wanted to make sure that Charlemagne would follow in Constantine's footsteps without making the same mistakes.