Between the fourth and tenth centuries, across most of western Europe, law, legal institutions, and legal procedures became Christianized, in the sense that Christian rhetorical tropes, ideologies, and existential perspectives infused legal expression and practices. Royal and imperial courts were sites for interweaving secular and ecclesiastical authority, and hence for interweaving secular and ecclesiastical law. Such interweaving found voice in “mixed assemblies,” that is, assemblies in which both higher clergy and secular nobility participated in judicial and legislative processes; documents issued under the name of a king or emperor also show the integration of secular and ecclesiastical law. Law was not exclusively developed and implemented at royal courts and assemblies: complementing governmental efforts to instantiate Christian law, the educated elite took an interest in law, both as a subject for study and as a resource for informing arbitration, prosecution, or defense of rights and privileges. One of the many streams of legal formation was the practice of collecting, compiling, and conserving decrees and judicial opinions that would, in time, constitute the core of the canon law of subsequent centuries.