Caldarium

[1][2] The boiler supplying hot water to a baths complex was also called caldarium.

A caldarium in both public and private baths followed a common plan which had three main parts.

[2] The common arrangement would include a warm-water bath -- usually called alveus, but also referred to as piscina calida or solium -- sunk into the floor, a semicircular alcove -- laconicum -- where bathers would sit in order to induce sweating, and in the middle of the room a vacant space -- sudatorium or sudatio -- meant for physical exercise before going to sit in laconicum.

[2] The bath's patrons would use olive oil to cleanse themselves by applying it to their bodies and using a strigil to remove the excess.

This was sometimes left on the floor for the slaves to pick up or put back in the pot for the women to use for their hair.