Battle between warring European peoples might have occurred a millennium earlier than previously thought.

The re-evaluation comes from a survey of a mass grave in northern Spain’s Rioja Alavesa region, south of Bilbao, home to the remains of 338 people – primarily males – and potentially one of the most important battle sites in Europe.

A research group led by archaeologist Dr Teresa Fernandez-Crespo examined the skeletons and found 77 previously undocumented traumas, which they found to be consistent with aggressive events.

Rather than being the site of a massacre, as was previously believed, the Rioja Alavesa burial site instead looks to be home to a large-scale conflict.

Along with flint arrowheads unearthed at the site which mostly showed signs of hitting a target, about a quarter of burials had suffered skeletal injuries, and about a tenth failed to heal.

Previously, archaeologists believed large conflicts between Europeans occurred during the Bronze Age, which began about 4,000 years ago.

But carbon dating performed on the Rioja Alavesa remains suggest burials 5,400-5,000 years ago, placing it within the late Neolithic period. The results are published today in Scientific Reports.

Rather than many small-scale raids involving a few dozen individuals that were common at this time, the large number of people buried at Rioja and the rate of injury sustained in their skeletal remains suggests far larger interhuman conflict, potentially prompted by population pressures or cultural practice structures between groups.

The overrepresentation of younger males also makes a massacre unlikely. Such murderous events typically reflect a more ‘natural’ human population reflecting both sexes across many age groups.

“The fact that 11 of 13 cases of arrowhead injuries are linked to males and that most skeletons showing association with isolated arrowheads with signs of impact are male, suggests that men were preferentially exposed to violence at a distance,” writes Fernandez-Crespo’s team.

“Injuries to the head also support their participation in close-contact encounters.”

Although skulls show evidence of trauma on all sides, there were a disproportionate number of frontal injuries, suggesting oppositional combat. The researchers noted numerous reasons why women and children may be underrepresented in a mass burial site, including intra-group conflicts, abductions and enslavement, however err on the side of male remains being prevalent due to their role in combat.

This is reflected by the research team, which writes “the fact that most unhealed injuries recorded in sexed individuals affect men suggests that many males acted as combatants and eventually died in battle and raids”.

“The distinction between unhealed and healed occurrences is of the highest importance when interpreting trauma in the skeletal record of mortuary sites. This is particularly relevant in cases where a large number of individuals are involved and the precision of absolute dating methods is limited.”