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 facade 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]