Sometime between 2880 and 2776 BCE, 15 family members were hastily buried together in a single pit, their shattered skulls telling a story of violent death. Yet someone interred the dead with the pottery, tools, and ornaments typical of a proper burial in their culture, a culture we know today by the name of its most common ceramic artifact: the Globular Amphora. And someone seems to have made the effort to put the closest family members alongside one another in the pit.

Today, the grave near the village of Koszyce in southern Poland is the only record of one particular act of brutal violence during a turbulent time in European prehistory.

Out of the blue

It seems that no one in the seasonal camp of pastoralists was prepared for the raiders. Nearly all of the dead are women and children. Though women in the past (and today) could be formidable fighters, no weapons are buried with them to suggest that was the case here. Almost none of their bones show signs of broken limbs raised in defense (known as parry fractures), so it doesn’t look like they went down fighting. Instead, most appear to have died from crushing blows to the back of their skulls, as if they’d been captured and executed.

“We have other mass graves and evidence of violence from this period, so it seems that Koszyce was not a single rare event,” Morten Erik Allentoft of the Natural History Museum of Denmark told Ars Technica. Like most people living in Central Europe at the time, the Globular Amphora group were probably cattle herders who moved across the landscape as the seasons changed. It’s a lifestyle with a lot of potential for conflict with other groups of herders, either over vaguely defined territorial borders or over possession of cattle.

“We know from ethnographic and historical sources that cattle raiding and other forms of livestock theft is very common cross-culturally in pastoral societies,” study co-author Niels Nørkjær Johannsen of Aarhus University told Ars. “We have every reason to believe that competing communities during this period would have taken another (unrelated) group’s livestock if they got the chance, and would sometimes pursue this as a systematic strategy.”

Sometimes raiders just wanted to swipe a few cattle; other times they wanted to weaken or wipe out a rival group. That might mean killing the men of fighting age and kidnapping the women and children, or it might mean wiping whole communities off the map. In this case, the raiders apparently considered wholesale slaughter more expedient than taking prisoners.

A dangerous time to be alive

Around this time, a new culture was spreading through Central Europe, carried westward by people related to the Yamnaya herders of the Eurasian steppes. Like the Globular Amphora people, we know the newcomers today only from the things they left behind, especially a style of pottery called Corded Ware. Allentoft, Johannsen, and their colleagues suggest that this new group of herders created population pressures and heightened competition for resources and grazing land. That sense of crowding fueled a surge in encounters like the massacre near Koszyce.

The raiders left behind no evidence of their presence (aside from their grisly handiwork), so archaeologists can't say who they were. They might have been a neighboring Globular Amphora group, but they could just as easily have been Corded Ware newcomers. If so, the mass grave at Koszyce could be a grim window into a massive demographic shift in Europe at the dawn of the Bronze Age.

DNA preserved in the bones and teeth of the dead at Koszyce suggests that they were most closely related to a population of Anatolian farmers who moved into Europe earlier in the Neolithic period, with some genetic links to earlier European hunter-gatherer peoples. Their genomes contained no trace of ancestry from the Eurasian steppes. But by the Bronze Age, DNA from the skeletons of ancient Europeans suggests that the Corded Ware people's genetic makeup had almost completely replaced the older Neolithic populations all across Europe. There could be a lot of reasons for that—intermarriage is one, less-violent possibility—but the mass grave of Koszyce opens the door for some haunting speculation.

“With our study and others, it seems more and more likely that this big change in the gene pool was facilitated, at least partly, by violence,” Allentoft told Ars Technica.

The family plot

When archaeologists sequenced DNA from the remains, it turned out that the men and boys, at least, were all related on their fathers’ side of the family. The Y-chromosomes of the males in the group all belonged to the same line of descent, or haplogroup. Mitochondrial DNA is passed from mother to child, and the 15 people in the grave had mitochondrial DNA from six different maternal lineages. That probably means that in Globular Amphora society, women joined their husbands’ family groups when they married.

In the end, their husbands may have buried them in a mass grave after the raiders had gone. The DNA sequences allowed the archaeologists to calculate the relationships between every pair of individuals in the group, and they found four nuclear families, mostly mothers and their children (fathers, and adult males in general, were conspicuously absent from the grave).

At first glance, the grave looks like a haphazard pile of bodies, but it turns out that someone made the effort to bury close family members closer together; one mother lay next to her five- and 15-year-old sons, and another lay alongside her teenage daughter and five-year-old son. One young toddler’s parents weren’t in the grave, but he was buried beside fairly close relatives, maybe aunts or grandparents.

“With four nuclear families tied together by various secondary relationships there are many relationships to honor, and it is clear that lots of effort has gone into this, and the people who buried them knew the deceased very well,” Allentoft told Ars Technica. “It's far from random where the people are lying.” Someone even took care to place the oldest people in the group near the center of the grave.

The grave contained a family, minus its menfolk, buried by people who obviously knew them. It’s impossible to say for sure but also easy to speculate that perhaps the men of the village were away when the raiders came (or, to take the uncharitable view, maybe they fled), and they returned in time to bury the dead as well as they could under the circumstances.

“This burial combines a commitment to give these individuals a proper burial with the necessity of a mass burial,” Johannsen told Ars Technica. “Perhaps the people who buried them were in a hurry?” We’re left to speculate about whether they were in a hurry to flee or to go after the raiders—or maybe just to put the tragedy behind them.

PNAS, 2019. DOI: 10.1073/pnas.1820210116;(About DOIs).