The gateways of the town built by Sargon at the foot of his palace mound were roofed with semicircular vaults.[283] In order to study their construction more closely, M. Place demolished one of these arches piece by piece, the one numbered three on his plan.[284] It was already condemned to destruction by the necessity for carrying off its sculptures. The total height from pavement to keystone, was twenty-four feet six inches, from the centre of the keystone to the springing of the arch itself was eight feet, the total width of the opening, measured at the feet of the caryatides, was fourteen feet four inches. The bricks had not been burnt in a kiln but they had been subjected to a prolonged desiccation. The system of construction was as simple as possible. The perpendicular side walls passed into the vault without any preparation, and the arch when complete had no inward projection and no structural ornament but the inner faces of the carefully placed voussoirs; as all the bricks were of the same size and shape something more than their slightly trapezoidal form was required to keep them in place, and a softer clay was used to bind them together. With the addition of this rude cement each brick became a long and narrow wedge and determined the curve of the vault in which it was placed. Some idea of the appearance of this triple arch may be formed from the illustration we have compiled from M. Thomas's elevation of an alcove in one of the harem apartments at Khorsabad (Fig. 90). This vault is not in existence, but its component parts were found among the ruins of Sargon's palace.[285] [Illustration: FIG. 90.--Interior of a chamber in the harem of Sargon's palace at Khorsabad; compiled from Place.] There is one detail in the decoration of these doorways that should be carefully noted. Wherever the architect makes use of a round-headed opening he reinforces its outlines with a kind of semicircular frieze, to which brilliant colours or bold reliefs would give no little decorative value. In what M. Place calls _portes ornees_, this ornamental archivolt is of enamelled bricks, in the subordinate entrances it is distinguished from the rest of the wall merely by its salience. In neither case, however, does it end in any kind of impost, it returns horizontally without the arch and forms an ornament along a line corresponding to the spring of the vault within. We give an example of this peculiarly Assyrian arrangement from one of the gateways at Dour-Saryoukin (Fig. 91). Nothing like it is to be found, so far as we know, among the buildings of any other ancient people. [Illustration: FIG. 91.--Return round the angle of an archivolt in one of the gates of Dour-Saryoukin; compiled from Place.]