The walls, with their gateways, which still encircle Avignon, were erected between 1348 and 1364 during the residence of the Popes in the city. These walls (Fig. 50.) do not represent a very important defensive work, even for the time when erected; they are neither sufficiently high nor are the towers of suitable construction for a really strong enceinte. They are rather an outwork in front of the palace, which was itself a citadel of impregnable strength. [Illustration: FIG. 50. PORTION OF CITY WALL, AVIGNON. _West side._] At Avignon, as in the South generally, and also in Italy the towers are square, and they are constructed with the side next the town left open, so that in case of being taken by an enemy they could not be held against the inhabitants. They are not built, as the towers on the walls of enceinte of the great castles were, of size and strength enough to stand an independent siege. The large square towers occur at pretty wide intervals, and intermediate smaller turrets are occasionally introduced to strengthen the curtains between them. These are composed of two plain buttresses with a pointed arch thrown across between them near the parapet, behind which there is a long machicolation on the same principle as those of the Palace. At the base of the wall, and between these buttresses, a bold slope or talus is introduced, with the double object of thickening the wall at a point where it might be attacked by sap, and also to intercept any stone balls or other projectiles thrown from the machicolation, and cause them to ricochet obliquely against “cats” or other engines brought up to assail the wall. The talus would of course be designed in every case of such a slope as might be best suited for defence, according to the nature of the lower part of the fortifications, whether a ditch or a rocky escarpment. The walls of Avignon were entirely surrounded with a wet ditch above 20 yards wide, and 15 feet deep below the crest of the counter-scarp. The ditch was supplied with water from the Rhone, the Sorgue, and branches of the Durance. Of the two last rivers the former joins the Rhone above and the latter below Avignon. The bottom of the ditch was paved to enable the sludge to be cleaned out. The ditches have now been completely filled up, and the spaces outside the walls converted into a public promenade. The towers, as above remarked, are for the most part of the square form generally adopted in the South, as distinguished from the round form which was usually employed in the North. The latter was considered safer, from its not presenting, like the square towers, any flat surface unprotected by the adjoining curtains against which miners could operate in comparative safety.