Submerged Stone Structures in the Far West of Europe During the Mesolithic/Neolithic Transition (Sein Island, Brittany, France)

Morpho-tectonic analysis of LIDAR data off Sein Island (France) revealed 11 submerged structures at significant depths. Dives conducted between 2022 and 2024 confirmed these are human-built granite structures, with the largest wall measuring 120 m long. Some structures appear to be fish weirs, others possibly protective. Based on relative sea level data, the dating of these structures was estimated to range from 5800 to 5300 BCE. These remains, unique at such depth, show Mesolithic human presence and advanced building skills, predating Neolithic megalithism in Brittany by 500 years. They offer valuable insight into maritime hunter-gatherer societies during the Mesolithic–Neolithic transition.