+STONE, CONCRETE, AND BRICK MASONRY.+ For buildings of an externally decorative character such as temples, arches of triumph, and amphitheatres, as well as in all places where brick and concrete were not easily obtained, stone was employed. The walls were built by laying up the inner and outer faces in _ashlar_ or cut stone, and filling in the intermediate space with rubble (random masonry of uncut stone) laid up in cement, or with concrete of broken stone and cement dumped into the space in successive layers. The cement converted the whole into a conglomerate closely united with the face-masonry. In Syria and Egypt the local preference for stones of enormous size was gratified, and even surpassed, as in Herod’s terrace-walls for the temple at Jerusalem (p. 41), and in the splendid structures of Palmyra and Baalbec. In Italy, however, stones of moderate size were preferred, and when blocks of unusual dimensions occur, they are in many cases marked with false joints, dividing them into apparently smaller blocks, lest they should dwarf the building by their large scale. The general use in the Augustan period of marble for a decorative lining or wainscot in interiors led in time to the objectionable practice of coating buildings of concrete with an apparel of sham marble masonry, by carving false joints upon an external veneer of thin slabs of that material. Ordinary concrete walls were frequently faced with small blocks of tufa, called, according to the manner of its application, _opus reticulatum_, _opus incertum_, _opus spicatum_, etc. (Fig. 48). In most cases, however, the facing was of carefully executed brickwork, covered sometimes by a coating of stucco. The bricks were large, measuring from one to two feet square where used for quoins or arches, but triangular where they served only as facings. Bricks were also used in the construction of skeleton ribs for concrete vaults of large span. +VAULTING.+ Here, as in the wall-masonry, economy and common sense devised methods extremely simple for accomplishing vast designs. While the smaller vaults were, so to speak, cast in concrete upon moulds made of rough boards, the enormous weight of the larger vaults precluded their being supported, while drying or “setting,” upon timber centrings built up from the ground. Accordingly, a skeleton of light ribs was first built on wooden centrings, and these ribs, when firmly “set,” became themselves supports for intermediate centrings on which to cast the concrete fillings between the ribs. The whole vault, once hardened, formed really a monolithic curved lintel, exerting no thrust whatever, so that the extraordinary precautions against lateral disruption practised by the Romans were, in fact, in many cases quite superfluous.