§212. Wall Facings.--Impervious to the weather though these walls were, they were usually faced with stone or kiln-burned brick (_laterēs coctī_). The stone employed was usually the soft tufa, not nearly so well adapted to stand the weather as the concrete itself. The earliest fashion was to take bits of stone having one smooth face but of no regular size or shape and arrange them with the smooth faces against the frame-work as fast as the concrete was poured in; when the frame-work was removed the wall presented the appearance shown at A in Fig. 59. Such a wall was called _opus incertum_. In later times the tufa was used in small blocks having the smooth face square and of a uniform size. A wall so faced looked as if covered with a net (B in Fig. 59) and was therefore called _opus rēticulātum_. A section at a corner is shown at C. In either case the exterior face of the wall was usually covered with a fine limestone or marble stucco, which gave a hard finish, smooth and white. The burned bricks were triangular in shape, but their arrangement and appearance can be more easily understood from the illustration (Fig. 60) than from any description that could be given here. It must be noticed that there were no walls made of _laterēs coctī_ alone, even the thin partition walls having a core of concrete. §213. Floors and Ceilings.--In the poorer houses the floor (_sōlum_) of the first story was made by smoothing the ground between the walls, covering it thickly with small pieces of stone, bricks, tile, and potsherds, and pounding all down solidly and smoothly with a heavy rammer (_fistūca_). Such a floor was called _pavīmentum_, and the name came gradually to be used of floors of all kinds. In houses of a better sort the floor was made of stone slabs fitted smoothly together. The more pretentious houses had concrete floors, made as has been described. Floors of upper stories were sometimes made of wood, but concrete was used here, too, poured over a temporary flooring of wood. Such a floor was very heavy, and required strong walls to support it; examples are preserved of the thickness of eighteen inches and a span of twenty feet. A floor of this kind made a perfect ceiling for the room below, requiring only a finish of stucco. Other ceilings were made much as they are now, laths being nailed on the stringers or rafters and covered with mortar and stucco. [Illustration: FIGURE 61. HUT OF ROMULUS] [Illustration: FIGURE 62. TILE FOR ROOF] [Illustration: FIGURE 63. TILE ROOF]