Such defects are sufficient to prove that these slabs were never meant to carry any great weight; far from affording a support to the wall behind, they required one to help them in maintaining their own equilibrium. On the other hand they protected it, as we have said above, from too rapid deterioration. At Khorsabad this stone casing is in very bad condition at many points, in the halls and passages of the outbuildings and in the courtyards adjoining the city gates for instance.[332] There the stones are only smoothed down, and their obvious purpose is merely to protect the crude brick within. The purely architectural origin of this system of casing is thus clearly shown. But the presence of these slabs set upright against the wall offered a temptation to the ambitious architect that he was not likely to resist. The limestone and alabaster of which they were composed afforded both a kindly surface for the chisel, and a certain guarantee of duration for the forms it struck out. In every Assyrian palace we may see that the king, its builder, had a double object in view, the glorification of the gods, and the transmission to posterity of his own image and the memory of his reign. To these ends the architect called in the sculptor, under whose hands the rudely dressed slabs took the historic forms with which we are familiar. Of all parts of the palace the doorways were most exposed to injury from the shocks of traffic, and we find their more solid plinths surmounted by higher and thicker slabs than are to be found elsewhere. These slabs are carved with the images of protecting divinities. Huge winged and man-headed bulls (Plate X)[333] or lions (Fig. 114), the speaking symbols of force and thought, met the approaching visitor. Sometimes a lion, reproducing with singular energy the features of the real beast, was substituted for the human-headed variety (Plate VIII).[334] These guardians of the gate always had the front part of their bodies salient in some degree from the general line of the wall. The head and breast, at least, were outside the arch. Right and left of the passage were very thick slabs, also carved into the form of winged bulls in profile, and accompanied by protecting genii. These latter divinities are sometimes grave and noble in mien, obviously benevolent (Figs. 8 and 29), sometimes hideous in face, and violent in gesture. In the latter case they are meant to frighten the profane or the hostile away from the dwelling they guard (Figs. 6 and 7). All these figures are in much higher relief than the sculptures in the inner chambers. [Illustration: FIG. 114.--Human-headed lion. Nimroud; from Layard.]