Hypocaust (Heat from Below) was a Roman engineering design that was used to heat both public and private buildings throughout the empire. The floor was raised on brick pillars and ventilation flues are built into the walls. Heat via a fire was produced and allowed to flow under the floors and out the flues heating the entire area through the floor. This radiant heat is clean and efficent. With the fall of Rome in the 5th Century, this technique of heating homes through the floor was lost in the Western World until the late 20th Century.