Pl.: caldaria
Often styled calidarium in Italian-language publications

The hot room of a Roman-style bathhouse. It could have different forms. In the early bathhouses, it often had a rectangular plan with one apsidal ending for the labrum (see schola labri). In later times, it was often cruciform or round. The room was heated by a hypocaust and its walls lined with tubuli, and had at least one warm water pool (alveus) for communal use. The caldarium was usually oriented to the south to benefit from the light and heat of the afternoon sun; for this reason, it often projected out of the main building.

Caldarium of the Faustina Baths at Miletus, Turkey (photo Konogan Beaufay).