=?Barrel Vaults?=--Another feature of the interior construction was the immense thickness of the walls, which varied from nine to twenty-five feet in solid brickwork. The object may have been to secure additional coolness, but this reason will scarcely afford a complete explanation of the extreme measurement. It is significant that the latter occurs in the halls of state which are also distinguished by their great length of 150 feet as compared with the width, 30 feet. When the narrow width of the halls is considered in relation to the immense thickness of the walls, it seems reasonable to conclude that the latter were intended to support the downward strain of barrel-vaulted ceilings. Additional probability is given to this conclusion by La Place’s discovery of great blocks, curved like the soffits of a vault, which had apparently fallen from a height. Moreover, in a bas-relief found by Layard in Koyunjik some of the buildings are shown to be roofed on the outside by domes. Accordingly, it is now the generally accepted belief that the usual style of ceiling employed by the Assyrians, was the barrel-vault. The origin of the latter may be found in the culverts by which the mounds were drained; but how, considering the scarcity of timber, it was possible to construct vaults of thirty feet span, is purely a matter of conjecture. It has been suggested that, while timber was costly, slave-labour was cheap, and it is possible that temporary structures of brick were erected as an underpinning to support the vault while in process of construction. On the other hand, we shall note later on that the architects of Gothic cathedrals, in countries where timber was scarce, adopted the method of rib-vaulting. Can it be possible that this invention was anticipated by the Assyrians? =Decorations.=--The walls of these halls of state were decorated up to a height of nine feet with sculptured slabs of delicate white alabaster or brilliantly yellow limestone, on which traces of paint have been discovered. As in the case of the Egyptian temples, scenes of everyday life, as well as of war or hunting, are represented, with a vividness that shows how closely nature had been studied by the sculptors, who, however, were more intent upon representing the spirit of the scene and preserving the feeling of decoration than in imitating nature. Thus, when they represented an archer, stretching his bow, neither the string nor the arrow was allowed to cut the lines of the figure. Both were shown as if the hand which held them were on the opposite side of the body. It is needless to say that this could not have been due to ignorance or negligence on the part of the sculptor, who otherwise proved his knowledge and observation of nature; but was a deliberate kind of conventionalisation, adopted, like the five legs of the colossal bulls, for a well-considered purpose--perhaps, not to interfere with the action of the figure.