A 1,500-year-old hilltop palace near Dijon still ran Roman-style underfloor heating

On a hilltop about 20 kilometers west of Dijon, archaeologists have found the remains of a 1,500-year-old building complex of palatial character that was still being heated from beneath the floor in the fifth century, a technique inherited from the Roman world. The site, the Montagne de Saint-Laurent at Mesmont in Burgundy, was occupied from the fifth to the early eighth century, long after Roman rule in Gaul had collapsed. Antoine Guicheteau of the French national archaeology institute Inrap leads the excavation.

Save more, waste less: The Cool Down’s newsletter sends smart, simple changes that help you and the planet in your everyday life.

Subscribe to The Cool Down →

We may earn a commission if you sign up.

Pillars, tile tubes and a raised floor

The evidence for the heating is physical and fairly plain. Excavators recovered small stone pillars, fragments of ceramic tubes and the remains of a raised floor, the three parts of a hypocaust in which a furnace sends warm air through the space beneath a room. In the classic Roman design, the floor rests on small pillars and the heat also rises through clay flues in the walls before leaving through the roof.

At Mesmont, an earlier fifth-century building had a heated floor and was later replaced in the sixth and seventh centuries by a residence about 22 meters long, with a central room, adjoining spaces and a front gallery. Weapons and clothing accessories from the residential area suggest wealthy, influential occupants. The raised floor and flues follow the hypocaust model that Roman builders used, here applied centuries after the empire’s authority in the region had faded. The building techniques, in other words, outlived the political system that had spread them, and the people who commissioned them still had access to the tile makers, masons and fuel supply that a working furnace demands.

Why underfloor heat marks a high-status site

The Inrap account of the Mesmont excavation is careful about what the heating proves. Such installations, it says, are characteristic of sites where high-ranking people lived and were able to finance such work, because they required specialized craftsmen such as brick and lime makers. The institute describes the summit as a built complex of palatial nature, which presents the palace label as an interpretation rather than a settled fact.

The dating rests on pottery, including a small lot of Argonne sigillata, and a series of radiocarbon analyses. Together they place construction in the fifth century and occupation until the early eighth century, with few major alterations.

In 2026 the dig also exposed a masonry building of about 15 by 12 meters west of the church, possibly with an upper floor, and detected a construction more than 20 meters long to the south whose width is still unknown. The buildings together cover several hundred square meters. Arkeonews’ coverage of the 1,500-year-old palace notes that the hill had been explored since the nineteenth century, but only excavations beginning in 2019 revealed how important the settlement was.

A church with more than 500 glass fragments

Beside the residence stands a large masonry church, about 27.5 meters long and 12.4 meters across at its widest, which may date to the fifth century. It has an apse and traces of a possible wooden screen separating the sanctuary from the congregation. More than 500 glass fragments have been recovered since 2019, and about 50 of them are flat cut pieces probably from windows, along with lighting equipment and glass vessels that suggest a finely furnished interior.

Metal detectorists have repeatedly looted the site, so metal objects are lost to the record. The wealth the excavators infer therefore rests on what remained, from glass and heating hardware to weapons, rather than on a full inventory.

Burgundians, Franks and the end of the hill

The region lay within the kingdom the Burgundians founded, which came under Frankish control in 534, during the era of the Merovingian dynasty. Medieval records tie the area to an administrative district called the pagus Magnimontensis, and Inrap links the sixth-century figure Sigo and the Gregorii family to it, though it does not tie them directly to the heating system. Historical sources also mention religious figures Gregory of Langres and his grandson Eustace.

The hilltop overlooks the Ouche Valley, and the finds from it, which run from weapons and clothing accessories to window glass, lamps and a church with a probable chancel screen, describe a community with real means. Pottery and radiocarbon dating show that occupation ran from the fifth to the early eighth century, a span of roughly three centuries that began as Roman rule was collapsing and ended as Frankish power consolidated. The settlement appears to have declined by the early eighth century, possibly as activity shifted to nearby Sombernon. The Arkeonews report quotes the broader conclusion that Mesmont was far from a simple hilltop refuge, and was instead home to wealthy families, religious buildings and a community. Excavations are continuing under a new three-year program that began in 2026, and Guicheteau’s team has not yet established the full width of the southern building or the identity of its occupants.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

Save more, waste less: Subscribe to The Cool Down →

We may earn a commission if you sign up.