The bather moved from warm to hot baths, through rooms of varying temperatures. Located under the floor, the heating system (hypocaust) located under the floor allowed the air, warmed by wood fires in adjacent vaults, to circulate between pillars of terracotta disks that heated the marble floor; terracotta pipes in the walls allowed the air to rise up to the ceiling. Water from the boiler fed the marble-tiled pools in the hot room (caldarium), and a large stone basin (labrum) contained cool water for the bathers’ use.