The Roman walls are an imposing defensive circle which was covered with blocks of travertine stone on the outer face and by walls and buttresses in the interior. During medieval times towers and walls were often incorporated into the construction of new buildings. Only some of the 20 original defensive towers remain; the first found at the entrance to the area and the Tour Fromage. Others include the Tour du lépreux, Tour du Pailleron, the 11th Century Tour Neuve, and the 13th Century Tower of Bramafan, a former residence of the Savoy viscounts.