For the warming of a house the Romans not only portable braziers with charcoal for fuel, but in the larger establishments there existed a system of "central" heating, by which hot air was conducted from a furnace in the basement through flues running beneath the floor and up through the walls, where its effect might be regulated by adjustable openings or registers. The only fixed fire-place in a town house was in the kitchen. From this the smoke was carried off by a flue, constituting to all intents and purposes a chimney. The belief that the Romans were unacquainted with such things as chimneys has been proved to be untrue. [Illustration: FIG. 40.--MANNER OF ROOFING WITH TILES.] The roofing, when constructed, as it most frequently was, in a gabled form, consisted of terra-cotta tiles arranged on a regular system. First came the flat layers, each higher row overlapping the lower. The descending edges of a row of these flat plates, as they lay side by side, were turned up into a kind of flange of about 2-1/4 inches in height, so that at the points of contact a ridge was formed down the roof. Over this line was laid a series of other tiles shaped into a half-cylinder, the lower end of each tile overlapping the next. By this means the rain was prevented from penetrating the crevice between the flanges. At the bottom, above the eaves, the line of semicircular tiles ended in a flower-like or mask-like ornament, which broke the monotony of the horizontal edge of the roof. After this description of what may be considered a representative Roman house, it is necessary to repeat that it is but typical. Many were considerably smaller, containing, for example, no peristyle. Many on the contrary were far more spacious and sumptuous, possessing more than one hall and more than one peristyle, and varying the nature as well as the number and position of those portions of the house. In exceptional cases the hall had no opening in the ceiling and therefore no basin below, but was covered with a simple gabled roof which shed the rain-water into the street. In exceptional cases also there was no "parlour" of the kind described a little while ago. The situation of the house, enlargements made after the main part was built, the joining of two houses into one, or other causes, often modified the rectangular and symmetrical appearance presented in the plan hitherto given. Such modifications are, however, better illustrated by a comparison of the plans of two well-known Pompeian houses than by any amount of verbal description. The first is that of Pansa, which forms the main portion of a whole block, smaller dwellings and shops unconnected with the Pansa establishment being built round and into it at various points. The arrangements of this house closely approach the normal or simple type described in this chapter. The second is the famous house of the Vettii, which departs somewhat freely from the customary disposition of apartments.