Fig. 51.—Fortress; from the Balawat gates, in the British Museum.
All this, however, was but negative evidence. The real solution of the problem was first positively suggested by the discovery of vaults in place, in the drains and water channels, and in the city gates. The bas-reliefs in which towns or fortresses are represented also support the belief that great use was made of arched openings in Assyria, and the countries in its neighbourhood (see [Fig. 51]). As soon as it is proved that the Assyrians understood the principle of the arch, why should it any longer be denied that they made use of it to cover their chambers? It is obvious that a vault would afford a much better support for the weight above than any timber roof.
In the course of the explorations, a probable conjecture was changed into complete certainty. The very vaults for which inductive reasoning had shown the necessity were found, if not in place, at least in a fragmentary condition, and in the very rooms to which they had afforded a cover—and here we must quote the words of the explorers themselves.
In the most deeply buried quarters of the building, the excavations were carried on by means of horizontal tunnels or shafts. "I was often obliged," says M. Place, "to drive trenches from one side of the rooms to another in order to get a clear idea of their shape and arrangement. On these occasions we often met with certain hard facts, for which, at the time, we could give no explanation. These facts were blocks of clay whose under sides were hollowed segmentally and covered with a coat of stucco. These fragments were found sometimes a few feet from the walls, sometimes near the middle of the rooms. At first I was thoroughly perplexed to account for them. Our trenches followed scrupulously the inner surfaces of the walls, which were easily recognizable by their stucco when they had no lining of carved slabs. What then were we to make of these arched blocks, also coated with stucco, but found in the centre of the rooms and far away from the walls? Such signs were not to be disregarded in an exploration where everything was new and might lead to unforeseen results. Wherever a trace of stucco appeared I followed it up carefully. Little by little the earth under and about the stuccoed blocks was cleared away, and then we found ourselves confronted by what looked like the entrance to an arched cellar. Here and there these portions of vaulting were many feet in length, from four to six in span, and three or four from the crown of the arch to the level upon which it rested. At the first glance the appearance of a vault was complete, and I thought I was about to penetrate into a cellar where some interesting find might await me. But on farther examination this pleasant delusion was dispelled. The pretended cellar came to an abrupt end, and declared itself to be no more than a section of vaulting that had quitted its proper place.... The evidence thus obtained was rendered still more conclusive by the discovery on the under side of several fragments of paintings which had evidently been intended for the decoration of a ceiling."[200]
It is clear that these curvilinear and frescoed blocks were fragments of a tunnel vault that had fallen in; and their existence explains the great thickness given by the Assyrian constructor not only to his outer walls, but to those that divided room from room. The thinnest of the latter are hardly less than ten feet, while here and there they are as much as fifteen or sixteen. As for the outer walls they sometimes reach a thickness of from five and twenty to thirty feet.[201] The climate is insufficient to account for the existence of such walls as these. In the case of the outer walls such a reason might be thought, by stretching a point, to justify their extravagant measurements, but with the simple partitions of the interior, it is quite another thing. This apparent anomaly disappears, however, if we admit the existence of vaults and the necessity for meeting the enormous thrust they set up. With such a material as clay, the requisite solidity, could only be given by increasing the mass until its thickness was sometimes greater than the diameter of the chambers it inclosed.
M. Place lays great stress upon the disproportion between the length and width of many of the apartments. There are few of which the greater diameter is not at least double the lesser, and in many cases it is four, five, and even seven times as great. He comes to the conclusion that these curious proportions were forced on the Assyrians by the nature of the materials at their disposal. Such an arrangement must have been destructive to architectural effect as well as inconvenient, but a clay vault could not have any great span, and its abutments must perforce have been kept within a reasonable distance of each other.
Taken by itself, this argument has, perhaps, hardly as much force as M. Place is inclined to give it. Doubtless the predilection for an exaggerated parallelogram agrees very well with the theory that the vault was in constant use by Mesopotamian architects, but it might be quoted with equal reason by the supporters of the opposite hypothesis, that of the timber roof.
Our best reason for accepting all these pieces of evidence as corroborative of the view taken by MM. Flandin, Loftus, Place, and Thomas is, in the first place, the incontestable fact that the entrances to the town of Khorsabad were passages roofed with barrel vaults; secondly, the presence amid the debris of the fragmentary arches above described; thirdly, the depth of the mass of broken earth within the walls of each chamber; finally, the singular thickness of the walls, which is only to be satisfactorily explained by the supposition that the architect had to provide solid abutments for arches that had no little weight to carry.