Hypocaust

A hypocaust is a system of central heating that produces and circulates hot air beneath the floor of a building, its name coming from Ancient Greek words meaning under and burnt. A furnace generated hot air and smoke that moved beneath a raised floor supported by stacks of pillars called pilae, and this heat rose through clay or tile channels called caliducts set into the walls, warming the floor and the room above before venting through outlets in the roof, with operators controlling temperature by adjusting the amount of wood fuel and by placing the rooms meant to be warmest closest to the furnace. The architect Vitruvius credited Sergius Orata with inventing the system around 80 BC, though the Temple of Ephesus is said to have been heated this way as early as 350 BC, and the Romans went on to use hypocausts widely in public baths and wealthy villas across Europe, North Africa and western Asia. Because it demanded constant attention to the fire and heavy fuel use, the hypocaust remained an expensive feature found mainly in large villas and public baths rather than ordinary homes, and while its use declined in western Europe after Rome's fall around 400 AD, the Eastern Roman Empire kept the technology going for much longer.