The penultimate chapter is about the reliquary shrine of Saint Charlemagne known as the Karlsschrein. It explores both the political and the religious significance of the monument and how the local convent, the city and the imperial court all participated in its making. By delving deep into the history of Aachen and its surrounding region, the ex-Kingdom of Lotharingia, Sulovsky shows how every single inconsistency was deliberately chosen to make a political or religious point. Thus, where previous scholars only focused on the major figures on the shrine, this book presents dozens of overlooked depictions both of symbolic animals and of humans, including representations of the local community. Moreover, where scholars struggled to find an exact purpose for the shrine’s appearance, the author makes it clear that the papal–imperial negotiations for the introduction of hereditary monarchy served as the foundation for the new vision of the Holy Roman Empire. Indeed, the Karlsschrein is shown to refer not only to Charlemagne’s foundation of the city and church of Aachen, and also of the Empire, but to the centuries-long papal–imperial alliance.

Decretals, epistolae decretales, are papal letters that have a claim to universal validity and clarify questions of Church law. Already in Late Antiquity, petitioners would submit legal or disciplinary questions to the Roman emperor, who in response would provide authoritative answers in imperial rescripts. Papal decretal law was the product of an analogous procedure. Private parties would ask the pope to adjudicate their disputes, and in response the pope would set forth authoritative answers in decretal letters. The oldest fully preserved papal decretal is by Pope Siricius (384–99). Only with the pontificate of Alexander III (1159–81), however, did the number of decretals skyrocket and, as a result, there take place the further legal development and elaboration of the ius novum. Just two generations after Gratian’s Decretum (c. 1140), papal legislative acts had developed and changed canon law like never before.