might be developed in many, as yet unknown, directions. If we put
ourselves at this point of view we shall see that Isidore and Anthemius,
the architects of St. Sophia, were the disciples and perpetuators of the
forgotten masters who raised so many millions of bricks into the air at the
bidding of Sargon and Nebuchadnezzar.[208]

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 Chaldaea 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]

[Illustration: FIG. 55.--Restoration of a