A pit full of 6,200-year-old skeletons is now the oldest known example of 'indiscriminate, mass killing'

• Archaeologists discovered 41 skeletons buried 6,200 years ago in a giant pit in Croatia.
• The victims, most of whom were unrelated, were executed at the same time.
• A new study suggests the grave is the site of the oldest documented massacre ever found.

A man in a Croatian village was digging a foundation for his new garage in 2007 when he uncovered a pit full of skeletons.

New research about the mass grave suggests the bones belong to 41 people - children and adults - who were killed together and buried 6,200 years ago in the modern-day village of Potočani. The study, published in the journal PLoS One, suggests it's the oldest documented massacre in the archaeological record.

Many of the victims, the analysis showed, had been stabbed in the head. After examining the bones and extracting DNA - a process that took years - the researchers concluded that most of the individuals in the 7-by-3-foot pit weren't related to one another, and that they ranged in age from 2 to 50. There was almost an equal number of males and females.

"This is the oldest known case of indiscriminate, mass killing that we know of," James Ahern, an anthropologist at the University of Wyoming who co-authored the study, said in a press release.

Many of the victims' skulls had multiple stab wounds

Ahern and his team were invited to the burial site in 2012, which is when they started inventorying the skeletons and determining the victims' ages, sex, and manner of death. They differentiated between men and women as well as adults and children via known, identifiable anatomical differences.

The researchers figured out that of the 41 skeletons, 21 were male and 20 were female. About half were children between the ages of 2 and 17.

Thirteen of the skeletons had injuries on the sides or backs of their heads: The skulls showed evidence of being stabbed, cut, or bludgeoned. Some skulls had up to four puncture wounds.

The bones of the other 28 victims didn't reveal how they died, but "their deaths were almost certainly violent," according to Ahern.

"Individuals could have been strangled, bludgeoned, cut or stabbed in soft-tissue areas or in manners that did not damage underlying bones," he said.

None of the victims had wounds on their faces or arms. Mario Novak, an archaeologist at the Institute for Anthropological Research in Zagreb and a co-author of the study, told National Geographic that this suggests they were immobilized and had their hands tied, since people tend to use their forearms to block incoming blows.

"They were not defending themselves," Novak said, adding, "I would say that this was a pre-planned mass execution."

Given the pit's location, archaeologists at first guessed these people may have been victims of a World War II skirmish. But they were wrong: After dating the bones and some pottery fragments discovered nearby, the researchers determined all 41 victims were buried at the same time in 4,200 B.C.E.

This suggests the dead were part of the Lasinja culture, some of Europe's earliest pastoralists and metal workers.

The murders are still a mystery

The researchers found no clues as to who killed the people in the pit, or why.

The fact that there were nearly the same number of men and women ruled out the idea that the victims died in "a battle between two armed forces," the study authors wrote.

DNA from 38 of the skeletons revealed that 11 were close kin, but the other 70% of the victims weren't related. So the killers weren't targeting a particular family either.

These findings, coupled with the wide age range of the dead, points to seemingly indiscriminate, systematic violence, according to Ahern.

The killers could have been rivals of the Lasinja people, or perhaps Lasinja themselves, Novak said.

One possible explanation for the mass killing could be some type of climatic upheaval. When the climate changes, resources like crops, livestock, and water can become scarce. If that scarcity overlaps with a population boom, it can prompt groups to try to take over others' territories and resources, Ahern said.

Researchers studying other mass killings in the archaeological record have come to similar conclusions. Take the sacrifice of more than 260 Chimú children and 460 llamas in ancient Peru, for example: Experts think the Chimú may have sacrificed children to placate angry weather gods during a season of heavy rain and flooding.

"Increases in population size cause groups to overextend their local resources and require expansion into other areas. Both climate change and population increase tend to cause social disruption and violent acts, such as what happened at Potočani, that become more common as groups come into conflict with each other," Ahern said.