Above the stone basement was a massive structure of crude brick, without any facing either of burnt brick or of stone.
The third kind of masonry at Khorsabad was found outside the main wall, and may have formed either part of the lining of the moat or a portion of a tower, which may have projected in advance of the wall at this point.

[PLATE LVIII., Fig.

1.] It was entirely of stone.

The lowest course was formed of small and very irregular polygonal blocks roughly fitted together; above this came two courses of carefully squared stones more than a foot long, but less than six inches in width, which were placed end-wise, one over the other, care being taken that the joints of the upper tier should never coincide exactly with those of the lower.
Above these was a third course of hewn stones, somewhat smaller than the others, which were laid in the ordinary manner.

Here the construction, as discovered, terminated; but it was evident, from the _debris_ of hewn stones at the foot of the wall, that originally the courses had been continued to a much greater height.
[Illustration: PLATE 58] In this description of the buildings raised by the Assyrians it has been noticed more than once that they were not ignorant of the use of the arch.