As already mentioned, the partition-walls of the rooms exhibit the same extraordinary solidity noticeable, alike in the outer walls of the palace and in those of the city, the thinnest being some ten feet thick. The massiveness of these partition walls bears out the theory that the roofs were not formed of wooden beams but of clay vaulting, and is thus an additional piece of evidence to that afforded by the absence of any trace of wood in the chambers themselves on the one hand and the discovery of fragments of wood in the doorways on the other; for the only available explanation and general _raison d’être_ of such thick interior walls is that vaulted roofs made of soft clay could only be supported by walls of more than ordinary solidity. Doubtless the vaulted roofing was also a determining factor in the shape and general contour which the rooms assumed, and it is to the dearth of wood suitable for building purposes, and the consequent use of clay for roofing as well as for other parts of the structure that we are to ascribe the narrowness of most of the chambers, which in truth resemble galleries more than halls or rooms. [Illustration: FIG. 9.—From an Assyrian Bas-relief. (After Layard, Ser. 2, Pl. 17.)] It must not however be supposed that all the rooms in Sargon’s palace or in the palaces of other Assyrian kings were one and all shaped like passages, or that they were one and all roofed with barrel-shaped vaults. Square rooms were discovered in the palace which we are discussing, some of which were of no mean dimensions and measured forty-eight feet each way; these clearly could not have been covered with barrel vaulting, while the difficulty of procuring timber of sufficient length would make itself felt more in the case of a large square chamber, than in an elongated gallery. The problem therefore resolves itself into an inquiry as to what other modes of roofing were adopted by the Assyrians apart from roofs made of wooden beams which were apparently only used in exceptional cases, and barrel vaults, which would have been out of the question in these large square chambers. It is here that the bas-reliefs adorning the walls of the royal palaces come to our aid. On one of these reliefs from Kouyunjik (cf. Fig. 9) are portrayed a number of buildings surmounted by domes of varying shapes and sizes, which prove conclusively that the Assyrians of Sennacherib’s time had evolved the art of constructing domed roofs, or perhaps we should say borrowed the art from their mother-country, as the principle of the domed roof seems to have been known in Babylonia in the pre-Sargonic times, for the American excavations at Bismâya have disclosed an oval-shaped room of the Sumerian period, provided with a domed roof of which the larger portions still remained, and without doubt the square chambers in Sargon’s palace at Khorsabad as well as those in the palaces of other Assyrian kings were roofed in this way. The buildings on the right (cf. Fig.