Around 3200 B.C.E., Stone Age farmers in Wales’s Preseli Hills built a great monument: They carved columns of unspotted dolerite, or bluestone, from a nearby quarry, then thrust them upright in a great circle aligned with the Sun. Exactly what the circle meant to them remains a mystery. But new research reveals that several centuries later, their descendants took down many of the giant stones and hauled them 200 kilometers to the Salisbury Plain, where they created what is still the world’s most iconic prehistoric stone monument: Stonehenge.