The legal underpinnings of the Western church experienced a major transformation during the twelfth and thirteenth centuries. This was a period in which papal legislation found its stride, in the form of conciliar decrees and papal decisions. Canon law collections provide a window into the rediscovery of Justinian's compilations, because they incorporated snippets of Roman law as it became available. Later papal legislation appears in other similar collections, including the Liber sextus of Pope Boniface VIII. Law professors at Bologna and elsewhere lectured on the collections of decretals, producing commentaries and summas. Medieval legal procedure relied heavily on both Roman and canon law. With respect to the laws of the church, the move towards complexity was also a product of the encounter with Justinian's Roman law. The thematic scope of canon law was in the main laid down with the Gratian's Decretum, which took its cue from the wide range of matters that French bishop Ivo treated in the Panormia.