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Heating Roman bath houses

Roman bath house at The Novium

A new vaulting technique for early baths in Sussex : the anatomy of a Romano-British invention


Roman Britain is not the first place that springs to mind when thinking of innovative vaulting techniques, yet it was the birthplace of a new type of heated vaulting system for bath-buildings using hollow terracotta voussoirs. The system underwent modifications but it was used for over two centuries and rarely left the province of Britannia. Its invention can be pinpointed to a particular place and group of builders - a rarity in antiquity. In this case, the voussoiurs were invented at a tilery believed to have been located on the coast of West Sussex, probably around Chichester.

The Westhampnett voussoir (named after two examples built into the fabric of a Saxon church in Westhampnett) was invented as part of a larger system for heating small baths. The robust nature of the double flue box-tiles must have been intended to support the fault of hollow terracotta voussoirs, a technique that had not been tried before. Once the idea spread and become more common during the 2nd century AD, the builders exhibited more confidence.

The popularity of the hollow voussoirs for the vaults of small baths probably lay in the potential fuel efficiency and cost reduction they could provide. A major part of the expense of having a private bath in one's villa was heating and maintenance. An inscription from the first half of the 2nd century AD which documents the gift of two baths to Altinum (near Venice) indicates that two-thirds of the annual operating costs were expected to go towards heating - for a private baths the costs could be recovered from bathing fees, but for a private baths they were simply the costs borne by the owner. In a cold damp climate (like Britain!) these costs could mount, so efficiency would have been a particular concern for the elite in Southern England who initiated the practice of building private baths at their villas.

What is so interesting about Roman bath construction in West Sussex?

Unlike Italy, Southern Gaul or even North Africa where the bathing habit was firmly established, Britain did not have a tradition of building baths or of brick and tile production before the Roman conquest in AD43. The invention of a new terracotta vaulting element for baths in a 'virgin' territory is all the more intriguing as it was introduced not by the Roman army, but by a civilian group of builders working in the Rome-friendly territory of the local Regni tribe.

The heating system devised by the Sussex builders that utilised voussoirs clearly influenced bath construction outside Sussex. Examples of tiles made in the distinctive Sussex fabric, including some Westhampnett voussoirs, have been found on 53 sites in London.

During the second half of the 1st century AD, London experienced a building boom as it grew into its role of provincial capital, and the newly devised heating system using the Westhampnett voussoirs was evidently imported for baths that were built during this period.

The earliest uses of the Westhampnett voussoirs appear to have been the well-appointed baths of Sussex villas that were at the vanguard of the emerging villa scene in Southern Britain. The baths at both Angmering and Fishbourne were decorated with Italian marble, stucco, painted plaster, mosaics and opus sectile, which all involved imported materials and skills. Both belonged to a series of 1st century AD villas in the territory of the Regni tribe. The innovations in bath construction were evidently made for wealthy landowners building for private use, though the finds of London-Sussex stamps in urban contexts at London, Chichester and Winchester suggest that the workshop did not confine itself to villas contexts.

Why invent this new system?

Why in a territory with no history of public bathing do we suddenly find the invention of hollow voussoirs? One factor was surely climate, which was colder (for longer) than that of Mediterranean lands. Heating the vaults would also have helped with condensation problems and it also could have reduced the costs of operation. Adding heated box-flue tiles to the walls could reduce fuel consumption by 20% in comparison to a bath with a heated floor alone. The addition of the hollow voussoir vault to the system could have increased the savings even more so long as it was properly insulated.

Who made these tiles and who built the baths?

Whoever invented the new heating system was plainly operating within the Roman technological mileu of bath-building and tile making, but there are also some indications of both indigenous and Gallic roots. Some of the Westhampnett voussoirs have graffiti on the unpatterned top side. Two are built into a church wall at Westhampnett : one has been deciphered as CALVI ('of Calvus'), indicting the maker had a typical Latin name, while the other is interpreted as T F P, probably the initials of a tria nomina (triple name) with T F suggesting T(itus) F(lavius), a person who had recently become a citizen under a Flavian emperor or who belonged to a recently enfranchised family. Three other Westhampnett voussoirs with identical graffiti, found re-used in a 4th century bath at Elsted near Chichester, have the letters BIIL. The two vertical marks after the B are a form of E that remained common in Gaul after it had gone out of common use in Italy. The graffito would then read BEL as the abbreviation of the maker's name, given that it occurs on three different voussoirs found together. The prefix Bel- is common in many Celtic names in Britain and Gaul - Belinatepus, Bellatorix, Bellognatus and Bellicus - but it is much rarer in Latin names. The evidence from the name would suggest Celtic roots, whether a local Briton of a Gallic immigrant. If from Gaul, he could represent one of the many craftsmen who migrated to Britain in the wake of the invasion, arriving with expertise in terracotta production techniques.

Ultimately, we do not know the precise origins of those who built this unique group of bath-buildings. What seems clear is that skilled and confident terracotta craftsmen dared to make the hefty flue tiles a structural component of the building. They were also confident heating engineers, not following a prescribed way of building baths imported from elsewhere. Initially they were hired by elite civilian patrons, probably of the Regni tribe. Thus they are unlikely to have been military experts. The little that can be gleaned from the graffiti and the roller dies suggests a Celtic background, possibly a mix of local Britons and Gallic immigrants, who saw an opportunity in the receptive lands of the Regni to fulfil a growing desire on the part of the elite to live the Roman lifestyle in their newly constructed villas.

Professor Lynne C. Lancaster

Department of Classics and World Religions

Ohio University

Extracts from an article to be published in the Journal of Roman Archaeology