Hypocaust
![Hypocaust under the floor in a Roman villa in Vieux-la-Romaine, near Caen, France](/Images/godic/202501/19/Vieux_la_Romaine_Villa_hypocauste5139.jpg")
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![Caldarium from the Roman Baths at Bath, in Britain. The floor has been removed to reveal the empty spaces through which the hot air would flow.](/Images/godic/202501/19/Caldarium5139.JPG")
![Wall flues for hot air circulation.](/Images/godic/202501/19/2006_0814HistriaTerme200603715140.jpg")
A hypocaust (Latin hypocaustum) was an ancient Roman system of underfloor heating, used to heat houses with hot air. The word derives from the Ancient Greek hypo meaning "under" and caust-, meaning "burnt" (as in caustic). The Roman Vitruvius, writing about the end of the 1st century BCE, attributes their invention to Sergius Orata.