The roots of modern Western legal institutions and concepts go back nine centuries to the Papal Revolution, when the Western church established its political and legal unity and its independence from emperors, kings, and feudal lords. Out of this upheaval came the Western idea of integrated legal systems consciously developed over generations and centuries. Harold J. Berman describes the main features of these systems of law, including the canon law of the church, the royal law of the major kingdoms, the urban law of the newly emerging cities, feudal law, manorial law, and mercantile law. In the coexistence and competition of these systems he finds an important source of the Western belief in the supremacy of law.