The ancient _cité_ of Carcassonne stands on the summit of a hill on the right bank of the river. It is still surrounded by its double wall of enceinte, studded with round and square towers, and dominated by the masses of the ancient castle, which rise boldly above the steep and rocky hillside, and present a sight as novel and picturesque as can well be imagined (Fig. 109). The site is naturally a strong one, and was doubtless occupied from a very early period as a primitive fortress. It afterwards became a Roman town, and was surrounded by the Romans with walls. The Visigoths, who were absorbed into the native population and continued the Roman civilisation, rebuilt the walls, some of which still survive, apparently on the Roman foundations and after the Roman manner. The Roman system of fortification consisted in erecting two walls to form an outer and inner face, the space between which was filled up with earth and stones. The level of the ground on the inside of the fortress was kept much higher than that on the exterior, and a broad parapet walk, easily accessible from the interior level, ran round the top of the wall, and was protected towards the outside with a parapet. At Carcassonne the more ancient parts of the curtains are composed of two walls built with small cubic masonry, alternating with courses of thin bricks (Fig. 110), the central space being, however, filled, not with earth, but with rubble masonry and mortar. The level of the ground is much higher next the town than towards the exterior. Some of the towers of the Visigoths still remain, and rise considerably above the curtains. These, like the towers of the Romans, are circular to the exterior and square next the city, on which side they are also open, both for the purpose of admitting of munitions being easily hoisted up to them from below, and also to render them useless in the hands of an enemy as against the town. Externally they are furnished with embrasures at the top, which were provided with a swinging wooden shutter for defence, to support the pivots of which stone hooks are inserted at the eaves. The top is covered with a pointed roof (_see_ Fig. 110). The towers were detached from the curtains by [Illustration: FIG. 110. CARCASSONNE--TOWERS AND CASTLE.] a pit or gap in the parapet walk where it adjoined them, so that each tower might form a separate post, and be defended independently. The lower part of the walls, being below the interior level of the ground, was peculiarly liable to be attacked by mining and battering, against which the defenders could make no direct resistance. The besiegers, as they knocked out parts of the wall, supported the superstructure in a temporary manner with wooden props, and when they had completed their mining operations, they set fire to the props, and the wall above fell and formed a breach.