Mass graves of soldiers from 1491 French siege discovered

In 1491, French forces laid siege to the city of Rennes. A team of researchers have now discovered two mass graves that contain the remains of over thirty soldiers who fought and died during the conflict.

From 2011 to 2013, a team from INRAP (National Institute for Preventive Archaeological Research) excavated the convent of the Jacobins, site of the future congress centre in Rennes Métropole. They uncovered two mass graves, which have 4 and at least 28 individuals respectively. The simultaneity of the deposits indicates a sudden episode: osteological analyses show that these soldiers, no doubt professional, died from stab wounds; radiocarbon analyses date the event from the mid-15th century to the end of the 16th century. All these criteria correspond to a single conflict: the War of Brittany (1487-1491).


INRAP worked with a multidisciplinary team of researchers from CNRS (Le Centre national de la recherche scientifique), the universities of Ottawa, Rennes 2, Toulouse III Paul Sabatier and the Max Planck Institute to learn about these soldiers and where they came from. This research is now published in two articles with the journal PLOS ONE.

The two pits excavated by INRAP in Rennes contained exclusively male skeletons. Large, mainly young, some are marked by perimortem trauma (wounds caused at or near the time of death). But what camps did the Jacobin burials belong to? Sulphur, strontium and oxygen isotopic analyses were conducted to determine the geographical origin of these soldiers.


© Rozenn Colleter / Inrap

The first grave shows that 3 of the 4 skeletons have a high probability of Breton origin. The fourth has old stab wounds that have scarred over. Its sulphur isotopic values suggest that this was a professional soldier, allied to the Breton camp. Indeed, his diet rich in animal proteins and his genomic characteristics favour the hypothesis of a noble soldier rather than a mercenary. The combination of isotopic and genetic analyses reveal that this nobleman had family ties in Brittany, had grown up far from his region of origin, but had returned to fight in the war threatening his independence.

The 28 subjects in the other pit belong to the French camp. Indeed, sulphur isotopic analysis on most of the individuals indicates a non-Breton geographical origin. The geographical origin models based on sulphur, strontium and oxygen isotopes suggest that these soldiers come from the north of the Paris Basin, the Poitou region, the Rhône valley and the Alps. These geographical origins support the rare historical data on the recruitment of French soldiers during this war. Some individuals would have a more distant geography, and would come from Castille, Aragon, England and the German Holy Roman Empire. The isotopic analysis of their diet indicates heterogeneous consumption of animal proteins, suggesting soldiers of varied social status.

The study of human bone remains from mass graves provides unique, first-hand historical insights into sparsely documented conflicts. This research shows that the cross-use of three isotopes can verify assumptions about alliances and recruitment strategies in wars, and completes deficient historical archives about the lives of ordinary soldiers.

Map of sulfur isotope distribution in Europe: shown in gray are the sulfur isotope values (from soldiers’ teeth and bones) compatible with the Breton region. © PLOS ONE CC-BY 4.0 International licence

The researchers develop geographical origin probability maps combining the sulphur, oxygen and strontium isotopes. They compiled 2,680 sulphur isotopic analyses from 221 sites across Western Europe in a database to observe the variations. These sulphur isotopic compositions across Europe are highly predictable and vary mainly with local deposits of sea salt and dust aerosols. Sulphur isotopes are highly complementary to those of strontium and oxygen and improve the accuracy of geographical attributions. The combination of these three isotopes then makes it possible to quantitatively and precisely assess the origin of the archaeological subjects, in particular making it possible to trace migratory flows.


In the 15th century, the Duchy of Brittany experienced a period of prosperity due to the policy of the Montfort family, creating a princely state independent of the kingdom. Several reasons led to the conflict: the desire of the King of France, following the Hundred Years’ War, to impose himself in Brittany; divisions within the Breton nobility and a ducal policy supporting revolts against the King of France. Moreover, since Duke François II did not have a male heir, the King of France, Charles VIII, claimed Brittany while the Duke positioned his daughters as the legitimate heirs. The war broke out in 1487. It involved many European forces: England, the Kingdoms of Castille and Aragon, the German Holy Roman Empire. The consequences of this conflict are still famous since it marked the end of Breton independence. The siege of Rennes in 1491 ended with the marriage of Duchess Anne of Brittany, then 14, to Charles VIII.

The article “The last battle of Anne of Brittany: Solving mass grave through an interdisciplinary approach (paleopathology, biological anthropology, history, multiple isotopes and radiocarbon dating),” by Rozenn Colleter et al., is published in PLOS ONE. Click here to read it.

The article, “Triple sulfur-oxygen-strontium isotopes probabilistic geographic assignment of archaeological remains using a novel sulfur isoscape of western Europe,” by Clément P. Bataille et al., is also published in PLOS ONE. Click here to read it.


Top Image: © Rozenn Colleter / Inrap