hould we find in it
vaults rivalling in age the arch in a tomb at Abydos which Mariette
attributes to the sixth dynasty?[294] Probably not. So far as we can judge,
Chaldaean civilization does not date from so remote a past as that of Egypt,
but it appears certain that the principles of the vault were discovered and
put in practice by the Chaldees long before the comparatively modern times
in which the segmental and pointed arches of Nineveh were erected. The
latter alone are preserved because they have been hidden during all these
centuries under the heaped-up ruins of the buildings to which they
belonged, while those of Chaldaea have been carried away piece by piece, and
their materials used again and again by the modern population of
Mesopotamia.

In spite, however, of the absence of such direct evidence, we may affirm
without fear that the Chaldaean architects soon discovered the principle of
the arch, and used it at least in its simplest and least complex forms. We
are led to these conclusions not only by their restriction to small units
of construction--a restriction which is sure, sooner or later, to lead to
the discovery in question--but also by induction from the monuments we have
just been studying. The arches under the hanging gardens of Babylon, the
vaults of the sewers and gateways, the domes that covered the great square
chambers in the Ninevite palaces--all these were derived, we may be sure,
from the ancient civilization. We cannot believe that such consummate skill
in the management of a difficult matter was arrived at in a day. The purely
empiric knowledge of statics it implies could only have been accumulated by
a long series of more or less happy experiments.

Thus only can we explain the ease with which the Assyrian builder
surmounted difficulties some of which would have puzzled a modern
architect, such as the pise vaults erected over spacious galleries without
any kind of centering, and the domes over square chambers, for which some
system of pendentives--that is, of arches or other intermediate forces--by
which the base of the cupola could be allied to the top of the supporting
wall, must have been contrived. The accurate calculation of forces between
the thrust of the vaults and the strength of the retaining walls, the
dexterity with which the curves employed are varied and carried insensibly
one into the other, the skill with which the artificial materials are
prepared for their appointed office