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 Graeco-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.

[Illustration: FIG. 52.--The Palace at Firouz-Abad; from Flandin and
Coste.]

[Illustration: FIG. 53.--The palace at Sarbistan; from Flandin and Coste.]

The corporations of architects and workmen must have preserved the
traditions of their craft from century to century, traditions which had
their first rise in the natural capabilities of their materials and in the
data of the problem they had to solve. The historian cannot, then, be
accused of going beyond the limit of fair induction in arguing from these
modern buildings to their remote predecessors. After the conquest of
Alexander, the ornamental details, and, still more, the style of the
sculptures, must have been affected to a certain extent, first by Greek art
and afterwards by that of Rome; but the plans, the internal