Of this kind are the triangular bricks used at the corners of walls, intended to give greater regularity to the angles than would otherwise be attained; and the wedge-shaped bricks, formed to be employed in arches, which were known and used by this primitive people.
The modes of applying these materials to building purposes were various.
Sometimes the crude and the burnt brick were used in alternate layers, each layer being several feet in thickness; more commonly the crude brick was used (as already noticed) for the internal parts of the building, and a facing of burnt brick protected the whole from the weather.
Occasionally the mass of an edifice was composed entirely of crude brick; but in such cases special precautions had to be taken to secure the stability of this comparatively frail material.

In the first place, at intervals of four or five feet, a thick layer of reed matting was interposed along the whole extent of the building, which appears to have been intended to protect the earthy mass from disintegration, by its protection beyond the rest of the external surface.

The readers of Herodotus are familiar with this feature, which (according to him) occurred in the massive walls whereby Babylon was surrounded.

If this was really the case, we may conclude that those walls were not composed of burnt brick, as he imagined, but of the sun-dried material.

Reeds were never employed in buildings composed of burnt brick, being useless in such cases; where their impression is found, as not unfrequently happens, on bricks of this kind, the brick has been laid upon reed matting when in a soft state, and afterwards submitted to the action of fire.