Nöbetçi Eczaneler
French marine archaeologists have discovered a submerged stone wall more than 7,000 years old on the seabed off western France, in what is thought to be the largest prehistoric underwater construction identified in French waters.
The structure lies in the Atlantic Ocean off the Île de Sein (Sein Island), at the western tip of Brittany, and is described in a study published in the International Journal of Nautical Archaeology.
Measuring close to 120 metres (400ft) in length at a depth of around 9m, the wall is accompanied by around a dozen smaller man-made stone structures from between approximately 5800 and 5300 BC, when sea levels in the region were significantly lower than today.
‘This is a very interesting discovery that opens up new prospects for underwater archaeology, helping us better understand how coastal societies were organised,’ said Yvan Pailler, professor of archaeology at the University of Western Brittany and a co-author of the study, speaking to Agence France-Presse.
The site was first identified in 2017 by retired French geologist Yves Fouquet, who noticed an unusually straight linear feature while examining laser-derived charts of the ocean floor. The scale and regularity of the feature suggested it was unlikely to have formed through natural geological processes.
Between 2022 and 2024, archaeologists carried out a programme of scientific diving to investigate the site, conducting a total of 59 individual dives by ten divers from the Société d’Archéologie et de Mémoire Maritime (SAMM).
The dives confirmed that the granite structures had been deliberately placed, although doing so was not without challenges. The waters off Île de Sein are subject to strong Atlantic swell and powerful tides, with rapidly changing currents and poor visibility making underwater work difficult.
‘Archaeologists did not expect to find such well-preserved structures in such a harsh setting,’ Fouquet told AFP.
The study’s authors suggest the structures may have functioned as fish traps, exploiting tidal movements to trap fish within their confines – a well-established practice, examples of which have been found in many locations across the walls.
The researchers also hypothesise that the walls may have been built to protect coastal areas from post-glacial sea level rise.
The authors state that the structures reflect ‘technical skills and social organisation sufficient to extract, move and erect blocks weighing several tons, similar in mass to many Breton megaliths’, adding that this level of technical capability predates the first known megalithic constructions in the region by several centuries.
The study also suggests the site may lie at the origin of local Breton legends of sunken cities, including the mythical city of Ys, believed to have been located nearby in the Bay of Douarnenez.
‘It is likely that the abandonment of a territory developed by a highly structured society has become deeply rooted in people’s memories,’ the authors write.
‘The submersion caused by the rapid rise in sea level, followed by the abandonment of fishing structures, protective works, and habitation sites, must have left a lasting impression.’
The complete study, ‘Submerged Stone Structures in the Far West of Europe During the Mesolithic/Neolithic Transition (Sein Island, Brittany, France)’ by Yves Fouquet, Jean-Michel Keroulle, Pierre Stéphan, Yvan Pailler, Philippe Bodénès, et al is published in the International Journal of Nautical Archaeology
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