The way in which these rooms were covered in has been much discussed. Sir Henry Layard believes only in flat roofs, similar to those of modern houses in Mossoul and the neighbouring villages. He tells us that he never came upon the slightest trace of a vault, while in almost every room that he excavated he found wood ashes and carbonized timber.[192] He is convinced that the destruction of several of these buildings was due in the first instance to fire. Several pieces of sculpture, those from the palace of Sennacherib, for instance, may be quoted, which when found were black with soot. They look like castings in relief that have been long fixed at the back of a fire-place. Long and narrow rooms may have been roofed with beams of palm or poplar resting upon the summits of the walls. As for the large halls, in the centre they would be open to the sky, while around the opening would run a portico, similar to that of a Roman atrium, whose sloping roof would protect the reliefs with which the walls were ornamented.[193] [Illustration: FIG. 50.--Present state of one of the city gates, Khorsabad. Perspective compiled from Place's plans and elevations.] As to this, however, doubt had already been expressed by an attentive and judicial observer like Loftus; who thought that the arch had played a very important part in the architecture of Mesopotamia.[194] As he very justly remarked, the conditions were rather different from those that obtained in the maritime and mountainous provinces of Persia; there was no breeze from the gulf or from the summits of snowy mountains, to which every facility for blowing through their houses and cooling their heated chambers had to be given; the problem to be solved was how best to oppose an impenetrable shield against a daily and long continued heat that would otherwise have been unbearable. Now it is clear that a vault with its great powers of resistance would have been far better fitted to support a roof whose thickness should be in some reasonable proportion to the massive walls, than a ceiling of bad timber. In our day the mosques, the baths, and many of the private houses of Mossoul and Bagdad have dome-shaped roofs. Without going as far as Mesopotamia, the traveller in Syria may see how intelligently, even in the least important towns, the native builder has employed a small dome built upon a square, to obtain a strong and solid dwelling entirely suited to the climate, a dwelling that should be warm in winter and cool in summer.