§369. The Caldarium.--The hot water bath was taken in the _caldārium_ (_cella caldāria_), which served also as a sweat bath when there was no _lacōnicum_. It was a rectangular room and in the public baths was longer than wide (Vitruvius says the proportion should be 3:2) with one end rounded off like an apse or bay window. At the other end stood the large hot water tank (_alveus_), in which the bath was taken by a number of persons at a time. The _alveus_ (Fig. 173) was built up two steps from the floor of the room, its length equal to the width of the room and its breadth at the top not less than six feet. At the bottom it was not nearly so wide, the back sloping inward, so that the bathers could recline against it, and the front having a long broad step, for convenience of descent into it, upon which, too, the bathers sat. The water was received hot from the furnace, and was kept hot by a metal heater (_testūdō_), opening into the _alveus_ and extending beneath the floor into the hot air chamber. Near the top of the tank was an overflow pipe, and in the bottom was an escape pipe which allowed the water to be emptied on the floor of the _caldārium_, to be used for scrubbing it. In the apse-like end of the room was a tank or large basin of metal (_lābrum_, _solium_), which seems to have contained cool water for the douche. In private baths the room was usually rectangular and then the _lābrum_ was placed in a corner. For the accommodation of those using the room for the sweat bath only, there were benches along the wall. The air in the _caldārium_ would, of course, be very moist, while that of the _lacōnicum_ would be perfectly dry, so that the effect would not be precisely the same.