Compact Construction. 113 and tend towards disintegration. They are not stable in them- selves, and in order to give them stability they must be kept in place by surrounding them with opposing forces which will effectually prevent their setting up any movement in the structure of which they form a part. This function is fulfilled by the wall in Egyptian architecture, which is consequently very thick, but the radiating arch never arrived at such a development- in Egypt as to lead to the adoption of any contrivance specially charged with the maintenance of vaults in a state of proper rigidity. The Egyptians not only employed the semicircular arch ; they made use, in a few instances, of the pointed form, and many of their underground buildings have roofs cut out of the rock in the form of a segmental vault. The fact that- these sepulchral chambers affected the aspect of vaulted halls, can only be explained by the supposition that a similar construction was common in the dwellings of the living.^ i^ 5- -Compact Construction. The methods employed in what we may call compact construction permit the use, in considerable quantities, of moulded clay mixed with chopped straw. This material was used in buildings which were homogeneous ; it was poured into a mould formed by planks, which was raised as the work progressed and the mixture dried. But the material had little strength, and was far inferior to those modern concretes which have the density and durability of the hardest stone. The Egyptians do not seem to have been acquainted with concrete proper, and un- burnt bricks did not differ essentially from pise. Such bricks, when placed one upon another after being imperfectly dried, combined, under the influence of the weather and their own weight, into one homo- geneous mass so that the separate courses became undistinguish- able. This latter fact has been frequently noticed in Assyria, by ^ Another explanation has been given of the employment of the vault in subter- ranean work. Marietta believed the arch to be symbolic, to signify the canopy of heaven, the heaven of Amen. One objection to this is the fact that the vault was not universal in tombs ; some of those at Beni Hassan have flat ceilings, others have coves. VOL. I. ' Q Fig. 80. — Granaries, from a bas-relief.
