§368. Heating the Bath.--The arrangement of the rooms, were they many or few, depended upon the method of heating. This in early times must have been by stoves placed in the rooms as needed, but by the end of the Republic the furnace had come into use, heating the rooms as well as the water with a single fire. The hot air from the furnace was not conducted into the rooms directly, as it is with us, but was made to circulate under the floors and through spaces between the walls, the temperature of the room depending upon its proximity to the furnace. The _lacōnicum_, if there was one, was put directly over the furnace, next to it came the _caldārium_ and then the _tepidārium_, while the _frīgidārium_ and the _apodytērium_ having no need of heat were at the greatest distance from the fire and without connection with it. If there were two sets of baths in the same building, as there sometimes were for the accommodation of both men and women at the same time, the two _caldāria_ were put on opposite sides of the furnace (see the plan in §376) and the other rooms were connected with them in the regular order, the two entrances being at the greatest distance apart. The method of conducting the air under the floors is shown in Fig. 172. There were really two floors, the first being even with the top of the firepot, the second (_suspēnsūra_) with the top of the furnace. Between them was a space of about two feet into which the hot air passed. On the top of the furnace, just above the level, therefore, of the second floor, were two kettles for heating the water. One was placed well back, where the fire was not so hot, and contained water that was kept merely warm; the other was placed directly over the fire and the water in it, received from the former, was easily kept intensely hot. Near them was a third kettle containing cold water. From these three kettles the water was piped as needed to the various rooms. The arrangement will be easily understood after a study of the plans in §§376, 378. [Illustration: FIGURE 173. SECTION OF CALDARIUM]