The ingenious Roman invention that sparked the ancient empire’s obsession with luxury

Think of Roman engineering, and it might be the grandest feats that first come to mind: the towering aqueducts bringing water to towns and cities, the amphitheatres filled with cheering crowds, and the paved roads that stitched the Roman empire together.

The hypocaust – the Roman system of underfloor heating – may be less staggering in its scale, but it remains one of the most recognisable features of Roman domestic life. Archaeologists still point to those distinctive stacks of bricks beneath villa floors as a mark of Roman sophistication.

“The hypocaust system is really important for us to think about when we consider Roman homes,” explains Dr Hannah Platts on the HistoryExtra podcast. “It was important to them: that it heated their baths and their other spaces.”

But they weren’t for everyone. Who owned homes with underfloor heating? And what did such comfort say about status and power?

“I should reiterate, having your own bathhouse or having a hypocaust was a luxury,” says Platts.

Rome’s underfloor miracle

At its simplest, a hypocaust worked by circulating hot air through a hollow space beneath the floor. A furnace, or praefurnium, was stoked outside the building; hot air from the furnace was funnelled into a network of small brick pillars (pilae) that supported a raised floor.

But it wasn’t just about heating the floor.

• Read more | How and why did the Roman empire fall?

“The hypocaust was used to heat houses via underfloor heating, but actually we’ve got a number of houses where we’ve got evidence of box flue tiles in the walls,” says Platts. “So we know that hypocausts could heat the walls of the rooms as well.”

In the context of ancient Rome this was engineering of incredible sophistication. Archaeological remains from sites such as Pompeii and Ostia, and across Roman Britain, show entire suites of rooms heated by the system.

Stepping barefoot on a mosaic floor, warmed from underneath, was quite literally to step upon Roman ingenuity.

From the baths to the villa

The hypocaust began as a public luxury, eventually exported to private homes. The earliest examples appeared in the great bath complexes (thermae) of the late republic and early empire. Roman baths were vast public leisure centres and required consistent, large-scale heating.

The first recorded Roman hypocausts date to the first century BC, developed under architects and engineers serving figures such as Marcus Agrippa, the ally and later son-in-law of the Roman emperor Augustus. Under Augustus himself, public bathhouses multiplied across Rome and its provinces. The technique soon spread to private villas, where the wealthy adapted public comfort for domestic display.

• Read more | The Roman invasion: whose side were the Britons on?

By the second century AD, during the reigns of emperors such as Hadrian and Antoninus Pius, the hypocaust had become a standard feature of elite architecture across the empire – from the Mediterranean heartlands to the frontier forts of Britain.

The price of luxury

But this warmth came at a cost. “We know that the idea of heating your house was really important, but it wasn’t for everyone,” says Platts.

“To have a hypocaust system in one’s house was a big sign of wealth. It would generally only have been present in examples of really opulent and wealthy dwellings: dwellings that, for example, might have their own private bathhouses.

“They didn’t even need to go to the general baths. They could just have fun in their own spaces.”

And, Platts says, what often goes forgotten is that maintaining heat from a hypocaust was hard.

• Read more | Everything you wanted to know about the Roman emperors

“It took significant effort to build [and] to maintain,” says Platts. Fires had to be constantly fed with wood, ash cleared away and airways cleaned.

“There’s engineering skill behind it too,” says Platts. “Not everyone is going to be able to build a hypocaust. There is a huge amount of skill behind that building process, and then you’ve actually got to be able to run the hypocaust and have it working. It really would’ve taken considerable finances to build a hypocaust within your house.”

The result was that the hypocaust became an unmistakable badge of wealth. Visitors entering a villa with warm floors knew instantly that they stood in the home of someone of status.

The Roman world of privilege and luxury

The hypocaust was one element within the broader picture of Roman luxury. For the upper classes, architecture, fashion, and food all worked together to display wealth and taste.

“What also would be luxuries could be the way in which people spent their fortunes in other ways,” Platts says. “I’m thinking about fashionable clothing, or elaborate jewellery or gemstones. Romans loved amber. They loved pearls. They had quite a thing for uncut diamonds – as we all might – and things that were imported: ivory imported from Africa, silks imported from towards China.”

The global reach of the Roman empire fed its appetite for exotic goods. To own these luxuries, to eat peppered dishes and dress in silk, was to embody the luxuries of empire.

“Anything like fine wines, exotic spices, was a really good way of showing your status,” Platts notes.

In this way, food became another way to demonstrate power. Enslaved servants circulated trays of imported delicacies from Britain, Syria and Africa, served to guests in rooms warmed by the hypocaust.

Living symbols of servitude

Luxury in Rome was also inseparable from labour, says Platts.

• Read more | Ancient Roman slavery: what was life like as an enslaved person?

“Whilst owning a slave in and of itself was not a luxury – Rome was a slave-based economy, and actually, even many of the really relatively poor households would likely have one or two enslaved people living under their roofs – the number of slaves you had, where they came from, and how skilled they were, that really was a sign of wealth and luxury.”

For the Roman elites, warm homes – and the people who kept them running – were signs of sophistication and wealth combined.

The hypocaust might not have been as spectacular as an aqueduct or as imposing as an amphitheatre, but it does symbolise a crucial fact of ethos of the Roman empire: it shows how innovative engineering served comfort for the wealthy as much as conquest on the frontiers.

Hannah Platts was speaking to Emily Briffett on the HistoryExtra podcast. Listen to the full conversation.