The concept of the “sacred palace” provides us with a key to understanding how Carolingian kings and emperors understood their roles in relation to religion and to the church, for they did not consider church and state to be fundamentally separate or mutually antagonistic domains. Furthermore, without understanding royal religious authority, we cannot properly interpret the role of public and royal penance during the reign of emperor Louis, Charlemagne’s son and successor. In this exploration of the wider context of the ruler’s religious authority, the interdependence of the ecclesia and the body politic in the ninth century is discussed. The French translation of this text was published as “Sacrum palatium et ecclesia. L’autorité religieuse royale sous les Carolingiens (790-840)” in Annales HSS, 58.6 (2003): 1243–69. It has not been updated to the present state of scholarship, but some suggestions for further reading have been added.