Yves Fouquet
Scientists believe that the wall was built on dry land, but ended up being submerged as sea levels rose.
Archaeologists claim to have discovered a remarkable submerged prehistoric stone wall on the northwest coast of France. The structure, built more than 7000 years ago by hunter-gatherers, was identified after years of research and is described in a new publication in the International Journal of Nautical Archeology.
The discovery began when the French geologist Yves Fouquet noticed a unusual linear formationnearly 400 feet long, while examining nautical charts near the Île de Sein, a small island off the western tip of Brittany. The formation stood out for its unusual straightness, which prompted a more detailed analysis by underwater archaeologists.
Detailed studies have revealed a substantial stone wall, about 20 meters wide at the base and approximately 2 meters high on average. The wall is topped and flanked by dozens of vertical granite slabsor monoliths, arranged in parallel lines and rising almost 2 meters above the flat ridge. Today, the structure is located approximately 9 meters deep in the Atlantic Ocean, explains .
When the wall was built, between approximately 5800 and 5300 BC, the landscape was very different. Sea level was about 7 meters lower than today, and the Île de Sein was approximately 14 times larger. Archaeologists believe the wall was on dry land, probably positioned between the island’s low and high tide marks.
Although its exact purpose remains unclear, researchers suggest that the wall may have been used by seafaring hunter-gatherers to catch fish during low tide or to protect coastal areas from flooding as sea levels gradually rose. The structure may even predate the famous Alignments of Carnac, the dense group of menhirs located in another part of Brittany.
“This is a very interesting discovery that opens up new perspectives for underwater archaeology,” said study co-author Yvan Pailler from the University of Western Britain.
In addition to the main wall, the team identified several other well-built granite structures nearby. Its size and construction quality suggest a work coordinated by a large group of peopleimplying that the region had abundant resources, especially fish, to support such efforts. Researchers believe the structures date from the transition from the Mesolithic to the Neolithic period.
The findings may also help explain persistent Breton legends about submerged cities, including the mythical City of Ys, which was lost under the sea near Douarnenez Bay. The authors suggest that the rapid rise in sea levels and the abandonment of coastal settlements may have left a lasting mark, preserved through oral traditions passed down over generations.
The discovery adds to growing evidence of sophisticated prehistoric engineering beneath Europe’s seas, including a 10,000-year-old underwater stone wall found off Germany’s Baltic Sea coast in 2024.
