We were lying within the dry cutting of a canal dug by Hârûn er Rashîd, and now called the Nahr el Ḳâim. It is connected with the Tigris by several cross-cuttings, over one of which we passed a quarter of an hour from the camping-ground, and found upon the further side the ruins of Ḳâdisîyah[116] (Fig. 119). They are nothing but a crumbling wall of sun-dried brick enclosing an octagonal area, but whether this space was ever covered with buildings it is difficult to determine[117]; I noticed, however, that the surface of the ground was piled into low mounds such as are left by the decay of sun-dried bricks. The octagon is far from regular. I paced the eight sides of the enclosing walls and found them to vary considerably from interior angle to interior angle, the smallest side being 565 paces, the largest 725 paces. Each angle is provided with an exterior round bastion, and at intervals of from twenty-eight to twenty-nine paces smaller round bastions project from the face of the wall. Six of the sides are broken by three gates apiece, one by four gates and one by two. The double-gated wall is the northern side of the octagon, and in the middle part of its length, between the two gates, there is a series of ten small vaulted chambers (3.55 m. wide by 3.65 m. deep) set against the interior face of the wall. The barrel vault of some of these chambers is still fairly well preserved. It is built of sun-dried brick laid in slices against the head wall on the Mesopotamian system, by which centering was avoided. Round the interior of the octagon, at a distance of thirteen paces from the wall, runs a shallow ditch, ten metres wide, having on its inner side a low mound which occupies a space about seventeen metres wide. The mound is no doubt the remains of a wall. Opposite each of the doorways in the outer wall, a causeway has been laid across the ditch. A wall and ditch upon the inner side of a strong fortification such as the enclosing wall of Ḳâdisîyah are singular features. They can scarcely have been intended for defence, indeed I am not certain that they extend round the whole enclosure. The ditch may have been a canal bringing water to the palace or fortress.