Archaeologists excavating a hilltop in northern France have uncovered a remarkable sequence of buildings, cellars, workshops and other remains documenting the transformation of an Iron Age settlement into a medieval upper town over more than 1,500 years.
The excavation is taking place on Montbellant hill in Tonnerre, in the Yonne department of Burgundy, where archaeologists from France’s National Institute for Preventive Archaeological Research (Inrap) are investigating approximately 750 square metres ahead of the construction of a detached house.
Beneath the relatively small plot, researchers have encountered more than two metres of archaeological deposits in places, preserving successive phases of occupation extending back to the first century BC.
The site lies less than 50 metres from another excavation carried out in 2024, which produced important evidence for the development of early Tonnerre from a Gallic oppidum through the Roman and medieval periods.
Together, the discoveries are providing archaeologists with an increasingly detailed picture of how settlement on Montbellant hill changed over approximately 1,500 years before the upper town was finally abandoned around the end of the Middle Ages.
The exceptional depth and complexity of the deposits mean archaeologists must excavate the site layer by layer, gradually working backwards through Tonnerre’s history until they reach the natural limestone.
The uppermost archaeological levels belong to the later Middle Ages and represent the final phases of intensive occupation on the summit of Montbellant.
Numerous pits and other cut features from this period penetrate earlier deposits, sometimes damaging or completely removing older remains.
Some are difficult to recognise when viewed from above because they were dug through layers of accumulated soil and colluvium. Their outlines become considerably clearer when they cut into the underlying limestone.
Archaeologists have therefore opened several sections through the deposits to understand the site’s complicated stratigraphy and establish how the different structures relate to one another.
As excavation progresses downwards, researchers expect to investigate each successive occupation phase until reaching the earliest known settlement, dating to the first century BC.
Large medieval building emerges
Among the most substantial discoveries so far is a large medieval building situated at the edge of the excavation.
Probably dating from the middle medieval period, the structure contains several rooms and shows evidence of repeated alterations during its lifetime.
One room incorporates an impressive cellar partly cut directly into the limestone bedrock.
Access was provided by a carefully constructed stone staircase, while the cellar itself cuts through pits belonging to earlier periods.
The cellar was deliberately filled during the Middle Ages, but archaeologists discovered that it stands beside an even older subterranean structure dating from the Roman period.
Part of this ancient cellar survives at a slightly higher level. A doorway was subsequently inserted after the medieval cellar had already been sealed, illustrating the complicated sequence of construction, modification and abandonment preserved within the building.
A second room has revealed another unusual architectural feature.
Although only partially excavated, it contained a vaulted entrance positioned towards the valley below.
At some point, the entrance collapsed into an older pit hidden beneath it. The resulting subsidence dragged part of the masonry wall and vault down into the cavity.
Several wedge-shaped stones, or voussoirs, from the arch have been recovered from the collapse.
Archaeologists also discovered an iron fitting still positioned between two facing stones, providing evidence that a wooden door once closed the entrance.
Evidence of Roman-era metalworking
Beneath the medieval structures, archaeologists are beginning to uncover an earlier phase of settlement dating from Antiquity.
Several buildings have been identified, some with portions of their walls still standing above their original floor levels.
One ancient building has been found associated with what appears to be a courtyard surface, although later medieval construction has damaged or obscured parts of the structure.
The widespread discovery of fragments of metallurgical slag across the excavation provides another clue to activities taking place on Montbellant during this period.
The concentration of this industrial waste suggests that a metalworking workshop may once have operated nearby.
Many of the ancient buildings remain only partially exposed, meaning their complete plans and functions have yet to be established.
Their location is already significant, however. Structures were constructed even along the steep slopes of Montbellant hill, suggesting that space was at a premium and that occupation was both dense and carefully organised.
Gallic settlement beneath the later town
Below the ancient buildings lies evidence of an even earlier settlement dating to the final centuries of the Iron Age.
Archaeologists have identified a structured occupation dating to the first century BC, when the hilltop formed part of a Gallic oppidum.
Although centuries of Roman and medieval building have heavily disturbed these earliest remains, pits and other excavated features survive beneath the later settlement.
Pottery and coins recovered from them confirm that an organised community occupied the summit before the Roman period.
These discoveries support evidence from the nearby 2024 excavation, strengthening the interpretation of Montbellant as a long-lived centre whose origins extend back more than two millennia.
The archaeological sequence suggests that rather than representing a series of unrelated settlements, the hill witnessed repeated occupation and redevelopment as buildings were constructed over, beside and sometimes directly through the remains of their predecessors.
Roman structures replaced or altered the Gallic settlement, while medieval inhabitants subsequently built houses, cellars and other features through the ancient remains.
Reconstructing the origins of Tonnerre
The excavation is particularly important for understanding the early urban development of Tonnerre.
Today, the summit of Montbellant appears far removed from the densely occupied environment revealed beneath the ground. During the Iron Age, Roman period and Middle Ages, however, archaeological evidence indicates that the hill supported substantial and sometimes intensive settlement.
The latest discoveries complement those made during Inrap’s 2024 investigation nearby, allowing researchers to compare neighbouring areas of the ancient hilltop settlement.
As archaeologists continue working down through the site’s unusually deep deposits, they expect to uncover further evidence of how buildings, streets, industrial activity and domestic spaces changed over successive centuries.
Eventually, the excavation should reach the earliest first-century BC occupation and provide another window into the Gallic community from which the later settlement developed.
The excavation will be exceptionally opened to the public on 3 September 2026, offering visitors an opportunity to see the layers of Tonnerre’s history while they are still being uncovered.
For archaeologists, the modest 750-square-metre development plot is proving to be something considerably larger: a densely layered record of the transformation of a Gallic hilltop settlement into the medieval town that preceded modern Tonnerre.
Header Image Credit : Jérôme Berthet, Inrap
Sources : Inrap
