More than 5,000 years ago, men, women and children with head injuries and gunshot wounds were buried in mass graves in Spain. Archaeologists have unraveled this complex web of skeletons, uncovering new evidence of ancient warfare, a new study has revealed.

The stone vault of San Juan ante Portam Latinam (SJAPL), located in the city of Laguardia in northern Spain, was first excavated in 1991. More than 300 skeletons were found in a single mass grave, radiocarbon dating them to between 3380 and 3000 BC; many of these were nested and in odd positions. Excavators also discovered dozens of flint arrowheads and knives, as well as stone axes and personal jewelry.

Researchers initially concluded that they had found evidence of a Neolithic massacre. But a new analysis of the skeletons by SJAPL found that these men were likely killed in separate raids or skirmishes that lasted months or years.

In a study published Thursday (November 2) in the journal Scientific Reports, first author Teresa Fernandez-CrespoThe archaeologist and his team from the University of Valladolid in Spain describe the healed and unhealed wounds on the SJAPL skeletons. They found a total of 107 cranial injuries, most of which were located in the upper part of the skull and likely corresponded to blunt force trauma, such as blows from stone maces or wooden clubs. Researchers found that men are almost five times more likely to suffer brain damage than women.

Injuries on the rest of the skeletons were also examined. The team identified 22 cases of injuries, mostly spiral or V-shaped fractures, to the extremities, as well as 25 injuries to other parts of the body. Like head injuries, these appear to disproportionately affect men; these men are almost four times more likely than women to have signs of bodily injury. Arrowhead wounds were also closely associated with male skeletons; This suggests that men are more likely to experience long-term violence than women.

Overall, juvenile and adult males buried at SJAPL represent 97.6% of unhealed injuries and 81.7% of healed injuries recorded in skeletons for which biological sex could be assessed. According to the study’s authors, this suggests that the mass grave “represents one or more ‘military layers’ that emerged as a result of wars and/or raids in which male participation was predominant.”

“We think we are seeing the outcome of a regional intergroup conflict in the SJAPL,” Fernández-Crespo told Live Science in an email. “Competition for resources and social complexity can be a source of tension between communities that can potentially escalate into deadly violence,” he said.

These Late Neolithic communities, each numbering a few hundred people, consisted mostly of farmers who grew wheat and barley and tended to domesticate herds of sheep, cattle, and pigs. But additional evidence of disease and stress the team found in Neolithic skeletons suggests that food shortages may have affected humans, potentially resulting from violence.

“This study makes strong evidence for interregional conflict in which male warriors died in battle,” bioarchaeologist Ryan Harrod of the University of Alaska at Anchorage, who was not involved in the research, told LiveScience in an email. “The fact that 338 people suffered more than non-fatal injuries suggests that many people survived their injuries, which may indicate that the regional conflicts were not epic battles or wars,” Harrod said.