A Massive Stone Wall Built 7,000 Years Ago Was Found Intact Beneath the Sea Off the Coast of France
An underwater find in Brittany reveals how ancient people faced a rising sea.
byTudor Tarita December 24, 2025
Edited and reviewed by Tibi Puiu
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Measurement of the height of a monolith; the rod held by the diver is one meter long. Credit: Yves Fouquet
Seven thousand years ago, people living on the Atlantic edge of Europe built a massive wall of stone where land met water. Today, that wall lies nearly nine meters underwater, still intact, stretched across a drowned valley off the coast of Brittany. Discovered near the Île de Sein at Brittany’s western edge, the wall reveals how prehistoric coastal people shaped their surroundings and coped with rising seas.
A Line on the Seabed
In 2017, retired geologist Yves Fouquet was studying high-resolution seabed charts created using lidar when he noticed something odd: a straight line cutting across an underwater valley.
“Just off Sein, I saw this 120-meter line blocking off an undersea valley. It didn’t make sense from a geologic point of view,” Fouquet told the BBC.
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3D view of TAF1 structures. View to the east showing the linearity of the structures and the dissymmetry of the north (left) and south (right) flanks. The brown colour visualizes the reefs permanently emerging above the current sea level. Credit: Yves Fouquet
Between 2022 and 2024, teams of divers returned to investigate. They confirmed that the feature was a human-built wall, 120 meters long, about 20 meters wide, and up to two meters high. It lies in an area swept by strong currents and heavy swells, conditions that make underwater work difficult and preservation unlikely.
More:
https://www.zmescience.com/science/archaeology/old-stone-wall-beneath-the-waves-france/