Neanderthals built one of the world’s oldest constructions – 176,000-year-old semicircular walls of stalagmites in the bowels of a cave in southwest France. The six structures are made of about 400 large , broken-off stalagmites, arranged in semi-circles up to 6.7 meters wide. The researchers think that the pieces were once stacked up to form rudimentary walls. All have signs of burning, suggesting that fires were made within the walls.