The Roman Baths could exploit the natural hot thermal waters, or be supplied with normal water from and aqueduct, which was then heated. Their main function was to take care of personal hygiene, with the added curative function of thermal waters. Roman citizens did not have houses with toilets and running water, so personal hygiene was cared for at the end of the working day in the Baths, usable free of charge or paying a modest political fee. It was a moment when you relaxed, met friends, before dinner which was the main meal of the day (fig. 1).

Fig. 1 - Ostia, Baths of the Forum (II cent. A.D.). Baths environments: in light blue the frigidarium; in yellow the tepidaria¸ in red the calidarium (from Pavolini 1983, re-worked by C. Tronchetti).

Some of the Baths environments were heated by an insulation system: the inner walls were surrounded by other walls leaving a cavity: hot air from the ovens passed through this and ran under the floor supported by small pillars (suspensurae, figs. 2-3). 

Fig. 2 - Heating system: from the oven the hot air flowed under the floor supported by suspensurae and, passing through holed tubuli in the walls, created warm insulation for the room (from Adam 1988, p. 293).

Fig. 3 - Reconstruction of a calidarium with two baths (from Adam 1988, p. 292).

This room also has baths and basins with water to cool yourself with (fig. 4). In unheated rooms, the baths are for immersion in cold water.

Fig. 4 - The reconstruction presents the apse of a calidarium with a basin of water to cool off with. It highlights the preparations for heating the environment (suspensurae) and the lighting from windows and skylights (from Macaulay 1978, p. 86).