From simple rock arches to Stonehenge, tens of thousands of imposing stone structures dot Europe’s landscapes. The origins of these megaliths have long been controversial. A new study suggests that large rock constructions first appeared in France and spread across Europe in three waves. The earliest megaliths were built in what’s now northwestern France as early as around 6,800 years ago, says archaeologist Bettina Schulz Paulsson of the University of Gothenburg in Sweden. Knowledge of these stone constructions then spread by sea to societies along Europe’s Atlantic and Mediterranean coasts, she contends in a study posted online the week of...