Researchers have found a complete stone wall submerged underwater, believed to have been built more than 7,000 years ago, specifically around 5000 BC.
This ancient wall stretches for 120 meters (approximately 390 feet), reaching a height of two meters and a width of nearly 20 meters. Originally built on land at the western end of the Brittany coast, specifically in the Île de Seine region, the wall now lies nine meters below the surface of the water due to rising sea levels over thousands of years.
There is now a scientific debate about the original purpose of this huge structure, with some suggesting it may have been a sea dam or a protective barrier built to try to stop the rising sea level, while others believe it served as a huge fish trap, making it one of the oldest known pieces of evidence of organized fishing practices in prehistoric times.
The sheer size and weight of the wall, estimated at around 3,300 tons, reflects a massive community effort. Its construction technique also demonstrates precision and advanced planning, with huge stone monuments (megaliths) first placed on the bedrock, and then smaller stones and slabs laid around them. This level of organization suggests a highly structured society, whether settled hunter-gatherers or early Neolithic groups.
The wall was first spotted using laser-guided mapping of the seabed, and then confirmed by marine archaeologists during dives that began in 2022. This discovery is the largest underwater structure ever found in French waters, and it is exceptionally well-preserved despite the passage of thousands of years.
The significance of this discovery extends beyond the stone walls themselves, as it has sparked hypotheses and connections to ancient local legends. Some have linked it to the legend of the lost city of Yss, a mythical city believed to have sunk off the coast of Brittany, suggesting that the memory of these lands being submerged and abandoned by organized communities may have been ingrained in the collective memory across generations.
This discovery highlights the unexpected engineering capabilities and social organization of Stone Age societies, and provides tangible physical evidence of how these early societies responded to the challenge of rising sea levels and major environmental changes.
