The city of Carcassonne stands upon a plateau commanding the valley of the Aude, the site of an ancient Roman _castellum_. In the sixth century it fell into the hands of the Visigoths, who fortified it. It increased considerably in extent during the tenth, eleventh, and twelfth centuries, but in the time of Simon de Montfort (1209) and of Raymon de Trancavel (1240) the _enceinte_ was not nearly so important as it became under St. Louis. By the middle of the thirteenth century the king had begun the construction of defensive works on a vast scale, and built the outer _enceinte_, which still exists, as may be seen on the plan (Fig. 167) taken from Viollet-le-Duc's _Cité de Carcassonne_. [Illustration: 168. CITY OF CARCASSONNE. RAMPARTS. SOUTH-WEST ANGLE] The primary object of the _enceinte_ was to secure the place against a sudden attack during the completion or enlargement of its interior defences. The additions of St. Louis, which were carried on by Philip the Bold, rendered Carcassonne impregnable in the general estimation. "As a fact, it was never invested, and did not open its gates to Edward the Black Prince till 1355, when all Languedoc had submitted to him."[61] [61] Viollet-le-Duc, _La Cité de Carcassonne_. [Illustration: 169. RAMPARTS OF AIGUES-MORTES, NORTH AND SOUTH] Oriental influences are equally evident at Aigues-Mortes. The Genoese Guglielmo Boccanera, who constructed the _enceinte_, was apparently familiar with the system of fortification adopted by the Crusaders in Syria. The machicolations which here make their first appearance in Languedoc (in the reign of Philip the Bold), proclaim the filiation of Aigues-Mortes to the Syrian fortresses. Italian influences are also perceptible in the square plan of the flanking towers. French architects had always preferred the round tower, as more solid in itself, and less open to attack from sappers, who, in advancing against a building of this form, were fully exposed to the missiles of the defenders from the curtains adjoining; while, on the other hand, the angles of the square tower gave a certain protection to assailants advancing against its front. [Illustration: 170. RAMPARTS OF AVIGNON. CURTAIN, TOWERS, AND MACHICOLATIONS] The ramparts of Avignon, which date from the fourteenth century, seem to have been constructed on Italian methods. The curtains are flanked by square towers, open towards the town, and surmounted by embattled parapets corbelled out from the walls, and machicolated so as to command their bases.