Here’s a wild one. It was first noticed a few years back, but a paper just got published. Off the coast of Brittany, France, near Île de Sein, divers have documented a vast submerged stone complex dating to roughly 5800–5300 BCE during the Late Mesolithic–Early Neolithic transition, when sea levels were lower. The largest feature is a 120 m (≈394 ft) long granite wall, flanked by 60+ upright monoliths and slabs reaching nearly 2 m (~6 ft) in height, uncovered through underwater surveys and LIDAR mapping. At least a dozen additional structures cluster nearby, some resembling smaller walls and lines of stones that may have acted as fish traps or barriers in the then-coastal landscape. The scale and craftsmanship imply complex planning, quarrying, transport, and coordinated labor among prehistoric coastal communities centuries before the region’s first known megalithic monuments. Rising seas would later submerge the site, preserving it under roughly 7–9 m (~23–30 ft) of water and offering new windows into early engineering and shoreline occupation.