Romans heated their homes and baths with underfloor central heating

Long before radiators, the Romans cracked central heating. Their system, the hypocaust — from the Greek for “heated from below” — was likely invented in the 1st century BC and became the beating heart of every serious bath-house and wealthy villa.

The trick was elegant. Builders raised the floor on short stacks of tile or stone pillars called pilae, leaving an open cavity underneath. A furnace, the praefurnium, was stoked through a stokehole, and its hot air and smoke were drawn through that cavity and then up the walls through hollow box tiles before venting out near the roof. Floors and walls became radiant surfaces, warming a room evenly from every direction.

The heat was even zoned. The room nearest the furnace, the steamy caldarium, ran around 40°C — hot enough that bathers wore wooden sandals to spare their feet — while the tepidarium further away idled near 30°C.

It was, in effect, climate control in the 1st century — run on firewood and constant human labor.

The catch was cost: a hypocaust devoured fuel and demanded someone tending the fire at all hours, so it stayed a luxury of villas and public baths. When the Western Empire fell, the engineering largely vanished from Europe, and comparable underfloor heating wouldn’t return for over a thousand years.