It is difficult to say how the Assyrians set about building these arches of crude brick, but long practice enabled their architects to use that unsatisfactory material with a skill of which we had no suspicion before the exhumation of Nineveh. Thanks to its natural qualities and to the experienced knowledge with which it was prepared, their clay was tough and plastic to a degree that astonished the modern explorers on more than one occasion. The arched galleries cut during the excavations—sometimes segmental, sometimes pointed, and often of a considerable height and width—could never have stood in any other kind of earth without strong and numerous supports. And yet M. Place tells us that these very galleries, exactly in the condition in which the mattock left them, "provided lodging for the labourers engaged and their families, and ever since they have served as a refuge for the inhabitants of the neighbouring villages. Workmen and peasants have taken shelter under vaults similar to those of the ancient Assyrians. Sometimes we cut through the accidental accumulations of centuries, where the clay, far from having been carefully put in place, had rather lost many of its original qualities. Even there, however, the roof of our galleries remained suspended without any signs of instability, as if to bear witness that the Assyrian architect knew what he was about when he trusted so much to the virtues of a fictile material."[202]
We may refer those who are specially interested in constructive methods to M. Place's account of the curious fashion in which the workmen of Mossoul will build a pointed vault without the help of any of those wooden centerings in use in Europe. In our day, certainly, the masons of Mossoul use stone and mortar, but their example none the less proves that similar results may once have been obtained in different materials.[203] A vault launched into mid-air without any centering, and bearing the workmen who were building it on its unfinished flanks, was a phenomenon calculated to astonish an architect. Taking everything into consideration the clay vaults of Khorsabad are no more surprising than these domes of modern Mossoul.[204]
We cannot say for certain that the Assyrian builders made use of domes in addition to the barrel vaults, but all the probabilities are in favour of such an hypothesis.
A dome is a peculiar kind of vault used for the covering of square, circular, or polygonal spaces. As for circular and polygonal rooms, none have been found in Assyria, but a few square ones have been disinterred. On the principal façade of Sargon's palace there are two of a fair size, some forty-eight feet each way. Thomas did not believe that a barrel vault was used in these apartments; the span would have been too great. He sought therefore for some method that would be at once well adapted to the special conditions and in harmony with the general system. This he found in the hemispherical dome.
All doubts on the subject were taken away, however, by the discovery of the bas-relief ([Fig. 43]) reproduced on page 145, in which we find a group of buildings roofed, some with spherical vaults, some with elliptical domes approaching a cone in outline. This proves that the Mesopotamian architects were acquainted with different kinds of domes, just as they were with varieties of the barrel vault.
It has been guessed that this bas-relief, which is unique in its way, merely represents the brick-kilns used in the construction of the palace of Sennacherib. To this objection there is more than one answer. The Assyrian sculptures we possess represent but a small part of the whole, and each fresh discovery introduces us to forms previously unknown. Moreover, had the sculptor wished to represent the kilns in which the bricks for the palace were burnt, he would have shown the flames coming out at the top. In reliefs of burning towns he never leaves out the flames, and in this case, where they would have served to mark the activity with which the building operations were pushed on, he would certainly not have omitted them. Again, is not the building on the left of the picture obviously a flat-roofed house? If that be so we must believe, before we accept the kiln theory, that the sculptor made a strange departure from the real proportions of the respective buildings. The doorways, too, in the relief are exactly like those of an ordinary house, while they bear no resemblance to the low and narrow openings which have been used at all times for kilns. Why then should we refuse to admit that there were vaults in Nineveh, when Strabo tells us expressly that "all the houses of Babylon were vaulted."[205]
Thomas invokes the immemorial custom of the East to support the evidence of this curious relief:—the great church of St. Sophia, the Byzantine churches and the Turkish mosques, all of which had no other roof but a cupola. In all of these he sees nothing but late examples of a characteristic method of construction which had been invented and perfected many centuries before at Babylon and Nineveh.
From the monuments with which those two great cities were adorned nothing but the foundations and parts of the walls have come down to our day; but the buildings of a later epoch, of the periods when Seleucia and Ctesiphon enjoyed the heritage of Babylon, have been more fortunate. In the ruins which are acknowledged to be those of the palaces built by the Parthian and Sassanid monarchs, the upper structures are still in existence, and in a more or less well preserved condition. In these the dome arrangement is universal. Sometimes, as at Firouz-Abad ([Fig. 52]), we find the segment of a sphere; elsewhere, as at Sarbistan ([Fig. 53]), the cupola is ovoid. Our section of the latter building will give an idea of the internal arrangements of these structures, and will show how the architect contrived to suspend a circular dome over a square apartment.[206]
These monuments of an epoch between remote antiquity and the Græco-Roman period were built of brick, like the palaces of Nineveh.[207] The exigencies of the climate remained the same, the habits and requirements of the various royal families that succeeded each other in the country were not sensibly modified, while the Sargonids, the Arsacids and the Sassanids all ruled over one and the same population.