In Roman times the shops, as the inner rooms of the house, were built lower, and over them small closed rooms were made, which were called by the same name as the open floor, pergula. These rooms were frequently accessible from the street by a stairway, and in such cases could be rented separately. In colloquial language, a man whose early life had been passed amid unfavorable surroundings was said to have been 'born in a room over a shop,'--_natus in pergula_. Shops were entered by means of small doors; the front was closed with shutters. These consisted of overlapping boards set upright in narrow grooves at the top and the bottom. A separate set of shutters was provided for the open pergula. XIII. WALLS, FLOORS, AND WINDOWS The walls were covered with a thick layer of plaster and painted; the preparation of the stucco, the processes employed in painting, and the styles of decoration are reserved for discussion in a later chapter. The floors were frequently made of an inexpensive concrete, consisting of bits of lava or other stone pounded down into common mortar. A much better floor was the Signia pavement, _opus Signinum_, so named from a town in Latium. This was composed of very small fragments of brick or tile pounded into fine mortar. The surface was carefully finished, and was sometimes ornamented with geometrical or other patterns traced in outline by means of small bits of white stone. In the Tufa Period a floor was often made by fitting together small pieces of stone or marble, and bedding them well in mortar. The colors are white and black,--slate is used in the floor of the atrium in the house of the Faun; sometimes also violet, yellow, green, and red appear with white and black. Pavements of square or lozenge-shaped and triangular pieces of colored marble and slate, like that in the cella of the temple of Apollo (Fig. 28), are occasionally found in houses. In the time of the Early Empire floors paved with larger slabs were not uncommon. The mosaics of the Pompeian floors--using the term mosaic in a restricted sense--may be divided into two classes, coarse and fine. In the former the cubes, _tesserae_, are on the average a little less than half an inch square. The patterns are sometimes shown in black on a white surface, sometimes worked in colors. The finer variety, in which the pictures appear, is not often extended over a whole room, but is usually confined to a rectangular section in the middle, coarse mosaic being used for the rest of the floor.