As in the interior arcade, the outer arches are slightly pointed and spring directly from the pilasters. The top of the exterior arches is ·30 metre above the level of the floor of the chemin de ronde. The chemin de ronde does not occupy the whole width of the core of the wall (Plate 3, Fig. 2). The passage is 1·90 metres wide. On the inner side, the wall is 1 metre thick and broken by the above-mentioned windows looking into the yard; on the outer side there is a series of recesses covered by ovoid arches. Each recess, 1·45 metres wide and ·40 metre deep, contains either a loophole window or a door. The loopholes, of which there are four between each tower, open on to the exterior of the palace and command a wide view of the desert. They are ·65 metre wide on the inside and narrow outwards to ·20 metre. On the inside they are covered by a lintel with an arched niche above it, on the outside they have a triangular head with a single upright stone placed within it, supporting the side stones of the triangle, and a small inverted triangular aperture above (Plate 8, Fig. 3 and Plate 10, Fig. 2). Each window recess is machicolated, there being an interval of ·20 metre between the outer edge of the floor of the recess (which corresponds with the outer face of the core of the wall) and the inner side of the arches of the exterior arcade. Through this gap an enemy standing at the foot of the wall could be attacked. Every fifth recess contains a door, ·75 metre wide, which gave access to a small round chamber hollowed out of the thickness of the tower. In the whole circuit of the wall not one of these tower chambers is intact, but enough remains to determine their construction (Plate 8, Fig. 2). Each chamber was covered by an ovoid dome, in the masonry of which there are traces of flat ribs. There was a loophole in the walls on either side, from which the defenders could cover the curtain wall between tower and tower, and it is reasonable to suppose that there must have been a third loophole fronting the desert. The loopholes were constructed in the manner already described. It seems probable that the towers exceeded the curtain walls in height; many of the towers show fragments of masonry higher than the present summit of the walls. The angle towers rose a story above the chemin de ronde and contained a second round chamber above the chamber on the level of the chemin de ronde. Traces of this second chamber remain in the north-east and in the south-west towers (Plate 8, Fig. 1). A stair was placed in each of the four angles of the castle yard (Plate 7, Fig. 1). The stairs, which were vaulted in a manner which will be described later (below p. 16), wound twice round the newel post before they reached the gallery of the chemin de ronde, and thereafter rose one story higher in order to reach the summit of the wall, and the upper chamber of the angle towers. It is probable that the summit of the wall was given a