Stonehenge, other ancient rock structures may trace their origins to monuments like this

Stonehenge may be the most famous example, but tens of thousands of other ancient sites featuring massive, curiously arranged rocks dot Europe. A new study suggests these megaliths weren’t created independently but instead can be traced back to a single hunter-gatherer culture that started nearly 7000 years ago in what is today the Brittany region of northwestern France. The findings also indicate societies at the time were better boaters than typically believed, spreading their culture by sea.

“This demonstrates absolutely that Brittany is the origin of the European megalithic phenomenon,” says Michael Parker Pearson, an archaeologist and Stonehenge specialist at University College London.

The origins of the megalith builders have haunted Bettina Schulz Paulsson since she excavated her first megalithic monument in Portugal nearly 20 years ago. Early on, most anthropologists thought megaliths originated in the Near East or the Mediterranean, whereas many modern thinkers back the idea they were invented independently in five or six different regions around Europe. The major hurdle, she says, has been sorting through the mountains of archaeological data to find reliable dates for the 35,000 sites, including carved standing stones, tombs, and temples.

“Everyone told me, ‘You’re crazy, it can’t be done,’” says Schulz Paulsson, a prehistoric archaeologist at the University of Gothenburg in Sweden and the study’s sole author. “But I decided to do it anyway.”

What she did was sift through radiocarbon dating data from 2410 ancient sites across Europe to reconstruct a prehistoric archaeological timeline. The radiocarbon dates came mostly from human remains buried within the sites. The study looked not just at megaliths, but also at so-called premegalithic graves that featured elaborate, earthen tombs but no huge stones. Schulz Paulsson also factored in information on the sites’ architecture, tool use, and burial customs to further narrow the dates.

The very earliest megaliths in Europe, she found, come from northwestern France, including the famous Carnac stones, a dense collection of rows of standing stones, mounds, and covered stone tombs called dolmens. These date to about 4700 B.C.E., when the region was inhabited by hunter-gatherers. Engravings on standing stones from the region depict sperm whales and other sea life, which suggests the precocious masons may also have been mariners, Schulz Paulsson says.

Northwestern France is also the only megalithic region that also features gravesites with complex earthen tombs that date to about 5000 B.C.E., which she says is evidence of an “evolution of megaliths” in the region. That means megalith building likely originated there and spread outward, she reports today in the Proceedings of the National Academy of Sciences .

By about 4300 B.C.E., megaliths had spread to coastal sites in southern France, the Mediterranean, and on the Atlantic coast of the Iberian Peninsula. Over the next few thousand years, the structures continued to pop up around Europe’s coasts in three distinct phases. Stonehenge is thought to have been erected around 2400 B.C.E., but other megaliths in the British Isles go back to about 4000 B.C.E. The abrupt emergence of specific megalithic styles like narrow stone-lined tombs at coastal sites, but rarely inland, suggests these ideas were being spread by prehistoric sailors. If so, it would push back the emergence of advanced seafaring in Europe by about 2000 years, Schulz Paulsson says.

“This seems quite plausible,” says Gail Higginbottom, an archaeologist at the University of Adelaide in Australia.

Parker Pearson says the study does a good job establishing that megaliths first arose in northwestern France, but it doesn’t quite rule out the possibility that some later cultures independently developed the idea.

Karl-Göran Sjögren, a fellow archaeologist at the University of Gothenburg, says he accepts that northwest France was among the first builders. But he isn’t fully convinced there aren’t still earlier megaliths yet to be uncovered, or more evidence that might push back the dates of some known megaliths. Future studies that include ancient DNA and other bioarchaeological evidence on population movements could clear things up, he says.