The urban organization of the medieval city of Vaison-la-Romaine is partly superimposed on the Gallo-Roman remains. They have often been reused for the construction of new buildings and, in particular, the foundations of Notre-Dame de Nazareth Cathedral built in the 11th century according to a basilica plan. With the expansion of Christianity, the medieval town, which has now disappeared, was first established on the right bank of the Ouvèze around its cathedral, the mother church of the diocese of Vaison that comprised some forty parishes belonging to the Papal States and Dauphiné.