As might have been expected nothing that can be called a structure of dressed stone has been discovered in Chaldaea;[164] in Assyria alone have some examples been found. Of these the most interesting, and the most carefully studied and described are the walls of Sargon's palace at Khorsabad. Even there stone was only employed to case the walls in which the mound was inclosed--a cuirass of large blocks carefully dressed and fixed seemed to give solidity to the mass, and at the same time we know by the arrangement of the blocks that the outward appearance of the wall was by no means lost sight of. All those of a single course were of one height but of different depths and widths, and the arrangement followed a regular order like that shown in Fig. 46. Their external face was carefully dressed.[165] [Illustration: FIG. 44.--Plan of angle, Khorsabad; from Place.] [Illustration: FIG. 45.--Section of wall through AB in Fig. 44; from Place.] The courses consist, on plan, of "stretchers" and "headers." We borrow from Place the plan of an angle (Fig. 44), a section (Fig. 45), and an elevation (Fig. 46). Courses are always horizontal and joints properly bound. The freestone blocks at the foot of the wall are very large. The stretchers are six feet eight inches thick, the same wide, and nine feet long. They weigh about twenty-three tons. It is astonishing to find the Assyrians, who were very rapid builders, choosing such heavy and unmanageable materials. The supporting wall became gradually thinner towards the top, each course being slightly set back from the one below it on the inner face (see Fig. 45). This arrangement is general with these retaining-walls. The average diminution is from seven to ten feet at the base, to from three to six at the top. The constructor showed no less skill in the use he made of his stretchers and headers. They not only gave him an opportunity of safely diminishing the weight of his structure and economising his materials, they afforded a ready means of adapting his wall exactly to the work it had to do. The headers penetrated farther into the crude mass within than the stretchers, and gave to the junction of the two surfaces a solidity similar to that derived by a wall from its through stones or perpenders. [Illustration: FIG. 46.--Elevation of wall, Khorsabad; from Place.] In describing this wall, M. Place also calls attention to the care with which the angles are built. "The first course," he says, "is composed of three 'headers' with their shortest side outwards and their length engaged in the mass behind. Two of these stones lie parallel to each other, the third crosses their inner extremities."[166] Thanks to this ingenious arrangement, the weakest and most exposed part of the wall is capable of resisting any attack.