Archaeologists have uncovered a submerged prehistoric stone wall off the northwest coast of France that may point to the existence of a long-lost settlement behind a local legend. The megalithic structure, estimated to be around 7,000 years old, was found nearly 30 feet underwater near the Île de Sein and may have served as a fish trap or a defensive barrier against rising seas.
The discovery suggests more underwater ruins could lie hidden in the region, offering rare insight into the period when Mesolithic hunter-gatherers began transitioning into permanent Neolithic communities. While Atlantis remains a myth, this find hints that other legendary sunken cities may have real prehistoric origins.
The wall was first identified by geologist Yves Fouquet through radar-based seafloor mapping, where it appeared as an unnaturally straight line along an underwater valley. Later LIDAR analysis revealed eleven human-made structures on the seabed, dated to between 5,800 and 5,300 BCE—at least 500 years older than Brittany’s earliest known megaliths.
Built from massive stones weighing a combined 3,300 metric tons, the structure shows signs of complex engineering designed to withstand storms, erosion, and rising sea levels. Its monoliths resemble the menhirs of inland Brittany and even the sarsens of Stonehenge, with some stones reaching nearly ten feet in height.
Researchers believe the site required advanced technical skill and strong social organization to construct and maintain. The findings have renewed interest in the Breton legend of the City of Ys, a mythical settlement said to have sunk beneath the sea nearby. According to Fouquet, the evidence raises the possibility that the legend may be rooted in real prehistoric events now hidden beneath the ocean.