For more than a thousand years, a lake 5,000 metres above sea level in the Indian Himalayas has been home to hundreds of human skeletons.

No-one has known how or why they got there.

It was previously thought they all died in a singular catastrophic event.

But a decade-long study into the human remains within and surrounding Roopkund — also known as Skeleton Lake — has revealed the victims had very different origins and were separated by more than a thousand years.

Local folklore described a pilgrimage to the nearby shrine of the mountain goddess, Nanda Devi, undertaken by a king and queen and their attendants, who were struck down by the goddess who was offended by their celebratory behaviour on the sacred journey.

Down the years there have also been suggestions the skeletons were the remains of an army, or merchants trapped in a blizzard, or that they were the victims of an epidemic.

Roopkund lake is cold enough to preserve DNA samples in the subcontinent. ( Wikimedia Commons )

Now, scientists believe there is an even more complex history than previously imagined.

While the majority of the 38 skeletons researchers used to extract DNA were of Indian origin, 14 appeared to be eastern Mediterranean, while one other individual appeared to be south-east Asian — just as far away from Roopkund.

"This finding shows the power of radiocarbon dating, as it had previously been assumed that the skeletons of Roopkund lake were the result of a single catastrophic event," said the study's co-author Douglas J Kennett of the University of California.

Hundreds of skeletons litter the surrounds and the depths of the lake. ( Atish Waghwase )

One sample of skeletons, which were already known to have perished up to 1,200 years ago, revealed variations of dating even within that group.

Some were dated to about AD 675-769, while another individual was dated more than 200 years after that.

The eastern Mediterranean sample — appearing to closely relate to present-day Crete and Greece — dated much more recently to around AD 1800.

Map Two samples originated from the eastern Mediterranean and southeast Asia, huge distances from Roopkund lake, centre.

The report says a likely explanation behind the older sample could be a mass death during a pilgrimage event.

But mystery still surrounds the newest sample of Mediterranean heritage, as well as the South-East Asian individual, who also dates to a more recent period.

Dietary analysis of the sampled skeletons backed up the DNA findings. ( Himadri Sinha Roy )

The report said an important direction for future investigation would be to find out if there were reports of large foreign travelling parties dying in the region over the last few hundred years.

Dietary analysis of the sampled skeletons backed up the DNA findings, confirming their diverse origins.

"Roopkund lake has long been subject to speculation about who these individuals were, what brought them to Roopkund lake, and how they died," senior author Niraj Rai said.

"It is still not clear what brought these individuals to Roopkund lake or how they died. We hope that this study represents the first of many analyses of this mysterious site."

The high altitude of Roopkund lake made it an ideal place for DNA to survive, and is one of the few places on the otherwise balmy subcontinent cold enough to preserve it for scientific analysis.