About 4,500 years ago, a large stone was placed on a sloping hill on England’s Salisbury plain. It was followed by another and another, until an entire henge had been formed, with its iconic “sarsen trilithons” towering over its human creators. But at some point after that construction work several millennia ago, the location of the original quarries were lost to time. Only recently were the Preseli Hills of Wales pinned down as the source of the henge’s smaller bluestones, which form a ring and a central horseshoe shape inside…
