vault has another strange singularity which at first is very
surprising. The whole structure has a sensible inclination in the direction
of its length, suggesting that some accident had happened to it in course
of erection. Such an explanation must be rejected, however, because at the
moment of discovery the whole arrangement was uninjured, and, moreover, the
filling of clay must have rendered any movement of the kind impossible. M.
Place's explanation seems the best. He thinks the slope was given merely to
facilitate the work of the bricklayers. The first course of voussoirs would
be sloped in this fashion, and would rest upon some mass of crude brick in
the centre of the building. The bricks of the second course would lean
against it, and their weight would be brought in to add cohesion and
solidity to the whole structure instead of being entirely occupied in
adding to the perpendicular thrust, while the ease with which they could be
placed without an internal support would be much increased. Assisted by
this simple expedient, two bricklayers with their labourers could build the
vault at a very rapid rate. We may believe that the notion of building in
this way would never have occurred to the Assyrian architects but for their
habit of dispensing with timber centres.

This slope had an effect upon the arrangement of the bricks which should be
noticed. In all other vaults, such as those of the city gates, the units
are laid upon their longest sides, and a vertical section shows their
shortest diameters. Here, on the other hand, the bricks stand on their
edges, and their largest surfaces are in contact, on each side, with the
next vertical course. If the full benefit of the natural cohesion between
one brick and another was to be obtained, this method of laying them was
absolutely necessary.

Internally, the drain we have been studying was four feet eight inches high
from the floor to the crown of the vault. Its width was three feet nine
inches, and its general slope very slight. It may be followed for a total
length of about 220 feet, after which falls of earth have carried away the
arch and the whole northern part of the esplanade, so that no trace of the
mouth by which it opened on the plain can be traced.

The other sewer described by M. Place may be more summarily dismissed. In
spite of their drawings and minute descriptions, explorers have not yet
succeeded in explaining the eccentricities of construction it presen