roman hypocaust heating systems made extensive use of fired clay elements: the space beneath the floor of a room to be heated was supported on robust pillars ("pilae"), usually made of small, square bricks mortared together, so that the heat from the adjacent furnace could circulate freely. in public and private bath-houses (essential to the roman way of life), heat was also carried up through the walls in flues made of interlocking box-tiles. though these were covered up by wall facings both inside and out, they were sometimes manufactured with quite elaborate geometric and even figural decoration. pipes for water and drainage were also often made of fired clay.