Marine archaeologists have confirmed the presence of a long submerged Stone Age wall and associated man-made structures off the coast of Brittany in western France.
The discovery predates the region’s earliest known Megalithic monuments by several centuries, according to newly published research.
The structure is some 120m long, 20m wide and averages 2m in height. It comprises large granite slabs and smaller stones, with upright monoliths set at regular intervals.
Some 12 additional smaller man-made stone features mapped in the vicinity are believed to be part of the same complex.
The site lies 1.9km west of Sein Island on a relatively shallow underwater plateau – average depth is 9m – submerged after post-glacial sea level rise.
The site was initially identified as one of interest in 2017 by geologist Yves Fouquet, who had noticed linear features on new seabed charts created using LIDAR (Light Detection and Ranging) technology.
Challenging conditions
French scuba teams including members of the Société d’Archéologie et de Mémoire Maritime (SAMM) conducted surveys between 2022 and 2024.
The researchers say that the combination of Atlantic waves, currents and harsh surface weather conditions proved challenging to systematic documentation. However, over the course of some 60 dives they were able to confirm that the features were human-made rather than natural seabed formations.
Based on the depth of the structures and associated geological data, the Fouquet-led team estimated that construction had taken place between about 5800 and 5300 BC, making the wall around 7,000 years old.
Sea levels were significantly lower at this time, between the Middle and New Stone Ages, and the area would have been formed of the coastal landscape rather than seabed.
The archaeologists say that the structures provide evidence of significant technical skill and social organisation among coastal communities that had proved capable of quarrying, transporting and erecting large stone blocks.
They conjecture that the wall and associated features might have been designed for use as fish-traps or tidal barriers on or near the shoreline.
The find “opens up new prospects for underwater archaeology”, say the researchers, providing insight into how prehistoric coastal societies organised labour and adapted to rising sea levels.
The findings have been documented in a study published in the International Journal of Nautical Archaeology. The archaeologists are continuing to examine the site in the hope of refining the dating of individual features and being able to place the structures in a broader cultural and environmental context.
Last year an 11,000-year-old early Middle Stone Age wall made up of some 1,500 stones stretching over almost 1km was discovered 21m beneath the Baltic Sea in Mecklenburg Bight.
