The enigmatic stone alignments in the Carnac region of Brittany, France, are among the most famous megalithic monuments in Europe - alongside Stonehenge, Menga, and the megalithic temples of Malta.
For the first time, it has now been possible to date parts of these alignments with a higher precision and gain new insights into their function.
This breakthrough results from a French-Swedish collaboration within the framework of the ERC-funded research project NEOSEA, led by the University of Gothenburg in partnership with the French excavation company Archeodunum and the University of Nantes.
"The alignments in the Carnac region now appear to be among the earliest megalithic monuments in Europe, with this section constructed between 4600 and 4300 cal BC. We have also confirmed the Bay of Morbihan as the earliest megalithic region in Europe",
says archaeologist Bettina Schulz Paulsson at the University of Gothenburg, who leads the NEOSEA project and is one of the researchers behind the new study published in Antiquity.
More than 3,000 standing stones stretch over 10 km in the region, from Carnac/La Trinité-sur-Mer to Erdeven, forming a unique concentration of megalithic alignments in a coastal landscape.
The archaeologists have excavated a previously unknown area, Le Plasker, bordering Carnac. In connection with this, they were able to carry out advanced analyses of the material, including radiocarbon dating - and statistical analyses of large series of radiocarbon dates, as well as sediment and charcoal analysis.
The rescue excavation at Le Plasker, located in the centre of Plouharnel, was conducted by the excavation company Archeodunum under the leadership of Audrey Blanchard, excavation director and researcher on the NEOSEA-project at University of Gothenburg, ahead of the development of a 7,000 m² business park. Better modern excavation technique combined with systematic sampling revealed numerous archaeological features.
"Thanks to nearly 50 radiocarbon dates and the application of Bayesian statistical modelling, we were able to reconstruct the site's history with unprecedented chronological precision", says Bettina Schulz Paulsson.
Bayesian modelling
Due to the acidic soils of the Morbihan, organic material - especially bone - rarely survives, which has long limited opportunities for radiocarbon dating in the region. Moreover, it is often impossible to confirm a connection between the dated charcoal samples and the erection of the standing stones and other methods, such as OSL dating (optically stimulated luminescence), often yield results that are too imprecise to support clear conclusions.
"However, with a sufficiently large dataset and Bayesian modelling, this challenge was overcome", Schulz Paulsson explains.
Several alignments of standing stones were dated to between 4600 and 4300 cal BC. While the stones themselves have been removed - either in historical times or prehistory - their foundation pits remain. These pits were aligned alongside hearths or cooking pits, suggesting that the stone lines may have been constructed in association with fire-related features. Whether these hearths were used for lighting, cooking, or feasting during the erection of the stones remains unclear. Further analyses of sediments and stone fragments are ongoing.
The site also revealed a monumental early tomb, constructed around 4700 cal BC directly above the remains of a Mesolithic hunter-gatherer hut.
The study is published in Antiquity as open access: "Le Plasker in Plouharnel (fifth millennium cal BC): a newly discovered section of the megalithic complex of Carnachttps://doi.org/10.15184/aqy.2025.10123
