Roopkund, a remote lake high in the Indian Himalaya, is home to one of archaeology’s spookiest mysteries: the skeletons of as many as 800 people. Now, a study published today in Nature Communications attempts to unravel what happened at “Skeleton Lake”—but the results raise more questions than answers.

In the early 2000s, preliminary DNA studies had suggested that the people who died at Roopkund were of South Asian ancestry, and radiocarbon dates from around the site cluster at 800 A.D., a sign that they all died in a single event.

Now, full genomic analyses from 38 sets of skeletal remains upend that story. The new results show that there were 23 people with south Asian ancestry at Roopkund, but they died during one or several events between the 7th and 10th centuries A.D. What’s more, the Roopkund skeletons contain another group of 14 victims who died there a thousand years later—likely in a single event.

And unlike the earlier South Asian skeletons, the later group at Roopkund had a genetic ancestry tied to the Mediterranean—Greece and Crete, to be exact. (An additional individual, who died at the same time as the Mediterranean group, had east Asian ancestry.) None of the tested individuals were related to each other, and additional isotopic studies confirm that the South Asian and Mediterranean groups ate different diets.

Why was a Mediterranean group at Roopkund, and how did they meet their end? Researchers don’t know and aren’t speculating.

“We have tried to answer all possible sources of genetic ancestries of [the] Roopkund skeletons but failed to answer why Mediterranean people were traveling to this lake and what they were doing here,” writes study co-author Niraj Rai, an archaeogeneticist at the Birbal Sahni Institute of Palaeosciences in Lucknow, India, in an email.

A “ghastly scene”

Roopkund’s strangeness unnerves even professionals. In the 1950s, one explorer described the site to an Indian radio station as a “ghastly scene that made us catch our breath.” And for decades, many scholars have tried to figure out who the men and women at Roopkund were and when they died.

The people’s cause of death has remained elusive. Death by battle is unlikely: The remains belong to both men and women, and no weapons or signs of combat violence have been found. The victims were also healthy when they died, which rules out a mass epidemic.

But what if a local folk song memorializes how the victims died? The song describes a royal procession during the Raj Jat—a pilgrimage held in the region every 12 years to worship the goddess Nanda Devi—that defiled the holy landscape with dancing girls. In response, an enraged Nanda Devi struck the group down with “iron balls” thrown from the sky.

One tantalizing possibility is that Roopkund victims were pilgrims who died during the Raj Jat after getting caught in a severe hailstorm. Parasols of a type used during the procession were reportedly found among the remains, and some individuals’ skulls bear unhealed fractures, perhaps a sign of large hailstones, the song’s lethal “iron balls.”

To check this scenario and others, an international team of researchers performed genomic analyses of the Roopkund remains. The team didn’t have expectations for who the people at Roopkund might have been, but signs of Mediterranean ancestry high in the Indian Himalaya came as a surprise.

“When we actually got the DNA back, it was super clear that some of these were not individuals with typical South Asian ancestry,” says Éadaoin Harney, study co-author and a researcher at Harvard’s department of organismic and evolutionary biology. “Definitely not something we were expecting at all.”

Did the Mediterranean group come for the Raj Jat pilgrimage and then stay at the lake long enough to meet their ends there? William Sax, head of Heidelberg University’s anthropology department and author of a book on the pilgrimage, says that this type of scenario “wouldn’t make any sense.”

Sax has made three trips to the lake, most recently in 2004 as part of a National Geographic television show, and says that modern pilgrims pay it little attention.

“When pilgrims get up to [Roopkund], they're scrambling because they have much farther to go, so they sort of stop and briefly show a bit of respect, if you will—but it's not and never has been terribly important for the pilgrimage itself,” he says. “It's kind of a dark and dirty place where you sort of nod your head and move on.”