Ancient undersea wall found off French coast

Rows of monoliths at the top of an ancient undersea wall off the Ile de Sein in Brittany, France. (Credit: Hal Open Science)

Divers have discovered a long-submerged wall some 7,000 years old under the sea off western France, scientists said Thursday.

Some 120 metres long, it was found off the Ile de Sein in Brittany along with a dozen smaller manmade structures from the same period.

“This is a very interesting discovery that opens up new prospects for underwater archeology, helping us better understand how coastal societies were organised,” Yvan Pailler, professor of archeology at the University of Western Brittany, told AFP.

He co-authored a study on the find, published in the International Journal of Nautical Archaeology.

The structures were first spotted by retired geologist Yves Fouquet in 2017 on charts of the ocean floor produced with a laser system.

Divers explored the site between 2022 and 2024 and confirmed the presence of the granite structures.

“Archeologists did not expect to find such well-preserved structures in such a harsh setting,” Fouquet said.

Dating from between 5,800 and 5,300 BC, they lie nine metres underwater and were built at a time when sea levels were much lower than today.

Researchers believe they may have been fish traps built on the foreshore, or walls to protect against rising seas.

The study says the structures reflect “technical skills and social organisation sufficient to extract, move and erect blocks weighing several tonnes, similar in mass to many Breton megaliths”, large stone arrangements used as monuments or for ceremonial purposes.

This technical know-how would predate the first megalithic constructions by several centuries.