Whatever may be thought of this hypothesis, there seems to be little doubt that the Assyrians knew how to pass from the barrel vault to the hemispherical, and even to the elliptical, cupola. As soon as they had discovered the principle of the vault and found out easy and expeditious methods of setting it up, all the rest followed as a matter of course. Their materials lent themselves as kindly to the construction of a dome as to that of a segmental vault, and promised equal stability in either case. As to their method of passing from the square substructure to the dome we know nothing for certain, but we may guess that the system employed by the Sassanids (see [Fig. 54]) was a survival from it. It is unlikely that timber centerings were used to sustain the vaults during construction. Timber was rare and bad in Chaldæa and men would have to learn to do without it. M. Choisy has shown—as we have already mentioned—that the Byzantine architects built cupolas of wide span without scaffolding of any kind, each circular course being maintained in place until it was complete by the mere adherence of the mortar.[209]
M. Place, too, gives an account of how he saw a few Kurd women build an oven in the shape of a Saracenic dome, with soft clay and without any internal support. Their structure, at the raising of which his lively curiosity led him to assist, was composed of a number of rings, decreasing in diameter as they neared the summit.[210] The domes of crude brick which surmounted many of the Kurd houses were put together in the same fashion, and they were often of considerable size. When asked by M. Place as to how they had learnt to manage brick so skilfully, the oven-builders replied that it was "the custom of the country," and there is no apparent reason why that custom should not date back to a remote antiquity. The Assyrians had recourse to similar means when they built the domes of their great palaces. They too, perhaps, left a day for drying to each circular course, and re-wetted its upper surface when the moment arrived for placing the next.[211]
Fig. 55.—Restoration of a hall in the harem at Khorsabad, compiled from Place.
From the existence of domes—which he considers to be almost beyond question—M. Place deduces that of semi-domes, one of which he assigns to the principal chamber of the harem in the palace at Khorsabad ([Fig. 55]). Feeling, perhaps, that this requires some justification, he finds it in a modern custom, which he thus describes:—"In the towns of this part of the East, the inner court of the harem is, as a rule, terminated at one of its extremities by a vault entirely open at one side, in the form of a huge niche. It is, in fact, the half of a dome sliced in two from top to bottom; the floor, which is elevated a few steps above the pavement of the court, is strewn with carpets and cushions so as to form an open and airy saloon, in which the women are to be found by their visitors at certain hours. This divan is protected from rain by the semi-dome, and from the sun by curtains or mats hung across the arched opening. This arrangement may very well be dictated by ancient tradition. It is well suited to the climate, a consideration which never fails to exercise a decisive influence over architecture."[212]
| Fig. 56.—Royal Tent, Kouyundjik. British Museum. | Fig. 57.—Tent, Kouyundjik. British Museum. |
And yet there would, perhaps, have been room for hesitation had no support to this induction been afforded by the figured monuments; for the inhabitants of the province of Mossoul have deserted the traditions of their ancestors in more than one particular. They have given up the use of crude brick, for instance, so far, at least as the walls of their houses are concerned. They have supplied its place with stone and plaster, hence their dwellings are less fresh and cool than those of their fathers. In such a question the present throws a light upon the past, but the two have distinctive features of their own, even when the physical characteristics of the country have remained the same. The best evidence in favour of the employment of such an arrangement in Assyria is that of the bas-relief. We there not infrequently encounter an object like those figured on this page. Sometimes it is in the midst of what appears to be an entrenched camp, sometimes in a fortified city. Its general aspect, certain minor details, and sometimes an accompanying inscription, permit us to recognize in it the marquee or pavilion of the king.[213] Now the roofs of these structures evidently consist of two semi-domes, unequal in size and separated by an uncovered space. If such an arrangement was found convenient for a portable and temporary dwelling like a tent, why should it not have been applied to the permanent homes both of the king and his people?
Arches still standing in the city gates, fragments of vaults found within the chambers of Sargon's palace at Khorsabad, the evidence of the bas-reliefs and the existing methods of building in Mesopotamia—all concur in persuading us that the vault played an important part in the constructions of Assyria, and consequently in those of Chaldæa; but we should not go so far as to say that all the rooms in the palace at Khorsabad and elsewhere were covered with barrel vaults, domes, or semi-domes. Our chosen guides, have, we think, allowed themselves to be a little too absolute in this particular; it is quite possible that by the side of the vaulted chambers there were others with wooden roofs. This conclusion is suggested partly by Sir H. Layard's discovery of considerable quantities of wood ashes in the palaces he excavated, partly by the evidence of ancient texts that wood was often used throughout this region to support the roofs at least of private houses. We may quote, in the first place, some remarks in Strabo's account of Susiana, which the Greek geographer borrowed from one of his original authorities: "In order to prevent the houses from becoming too hot, their roofs are covered with two cubits of earth, the weight of which compels them to make their dwellings long and narrow, because although they had only short beams, they had to have large rooms, so as to avoid being suffocated." This same writer, in speaking of these roofs, describes a singular property of the palm-tree beams. The densest and most solid of them, he says, instead of yielding with age and sinking under the weight they have to support, take a gentle upward curve so as to become better fitted than at first for the support of the heavy roof.[214]