The baths were made to be very attractive and striking places. Although most of the decorations have not survived, many writers commented on the luxury of the bathhouses, describing them with words such as, “well-lighted, lovely mosaics, airy rooms with high vaulted ceilings, silver faucets and fittings, and paintings and colored marble panels.” There was also a large entrance or meeting area, where people could walk, talk, or sit on seats around two large fountains. Roman engineers invented a system of heating the baths called thehypocaust. Pillars and spaces were left inside the walls so that hot air from the furnace, or praefurnium, could circulate and flow through the space in the walls. Rooms that required the most heat were placed closest to the furnace and the heat could be increased by adding more wood to the furnace. Many heated rooms and pools were positioned to make the most of the heat of the sun. At the Baths of Caracalla, the hot room was an enormous hall that was one hundred and fifteen feet wide with a pool three feet deep.In order to heat it, approximately fifty large furnaces were needed as well as millions of fireproof terracotta bricks or special bricks called tegulae mammatae. Bathhouses also had largepublic latrines, usually with marble seats over channels whose continuous flow of water that established the first “flush toilets.” These toilets were a vital part of the plumbing system as well as another common area in which to sit and talk. There was a continuous water flow underneath the seats. A shallowwater channelin front of the seats providedsponges attached to sticksfor people to wipe themselves.