The hill on which La Cité stands has been fortified across the centuries – by Gauls, Romans, Visigoths, Moors and Franks. In the 13th century, the walls protected one of the major Cathar strongholds. Once Roussillon was annexed to France in 1659, Carcassonne, no longer a frontier town, sank into slow decline. By the 19th century La Cité was simply crumbling away. It was rescued by the elaborate intervention of Viollet-le-Duc, who also set his controversial stamp upon, for example, the cathedrals of Notre Dame in Paris and Vézelay in the Massif Central.