inear 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 wi