Famously, the Fourth Lateran Council took place in 1215 and offered a bold new wave of papal legislation. Importantly, the Council confessed cum petro, with Peter Lombard. This was an unprecedented endorsement of a scholastic theologian. By confessing cum petro, the papacy placed Peter Lombard's Sentences at the heart of its bold reforming agenda. There has been very little historical analysis of the meanings of this endorsement. This article will attempt to situate the logic of this endorsement within the larger context of the Council, as well as the increasing formalisation of the Schools of Paris, which culminated in the founding of the University of Paris in that same year.