An ancient burial site, including an oddly shaped quartz stone covering the face of one of the newly uncovered human skeletons, has been discovered at the mysterious Plain of Jars, an archaeological site in remote central Laos littered with thousands of stone vessels.
The new findings could help researchers solve the long-standing puzzle of why the stone jars were scattered across this part of Laos.
When it was found, the skull beneath the quartz adornment appeared to be looking through a large hole in the stone, said Dougald O’Reilly, an archaeologist at the Australian National University (ANU), who led a team of scientists on a joint Laos-Australian expedition to the Plain of Jars in February. [In Photos: Exploring the Mysterious Plain of Jars Site]
"When we excavated it, the skull was actually looking out through that perforation. It was quite interesting, but whether it was done purposefully is difficult to know," O’Reilly told Live Science.
The burial site is estimated to be 2,500 years old, and was found when researchers from ANU, Monash University in Australia and the Laos Ministry of Information, Culture, and Tourism, spent four weeks mapping and excavating the ground around a group of the massive carved stone jars that dot the landscape.
More than 90 jar sites — some with up to 400 stone jars measuring as tall as 10 feet (3 meters) high — are spread across foothills, forests and upland valleys of this remote region.
The members of the Laos-Australian expedition worked at the most accessible site, known as Jar Site 1, located a few miles outside the city of Phonsavan, in Xiangkhoang province in central Laos. The researchers plan to explore a second, more remote jar site next year.
The Laos government hopes to develop Jar Site 1 as an archaeological center and UNESCO World Heritage site, to protect the unique Plain of Jars landscape and to stimulate scholarship and cultural tourism in the area.
O’Reilly said the latest expedition was the first major effort by archaeologists since the 1930s to visit the site, in an effort to understand the purpose of the jars and who created them. Since that time, however, some archaeologists have undertaken important work at the Plain of Jars, mainly on their own. [The 7 Most Mysterious Archaeological Finds on Earth]
The latest team of around 11 researchers worked together to compile the first comprehensive scientific study of one of the jar sites, including a GIS (geographic information system) map recording the precise location of each of the jars, stone disks and quartz stone markers scattered over the site.
The largest jars weigh more than 10 tons (9,000 kilograms), and a big part of their mystery is how they got there.
"There are a few well-known quarry sites where the jars were sourced and then brought across the landscape, about 8 to 10 kilometers [5 to 6 miles] to the jar sites," O'Reilly said. "So there's a huge amount of effort involved in moving them — one would have to speculate that elephants must have been involved, given the incredible weight of the jars."
And carving the massive jars would have been no easy task for primitive peoples with iron tools, he added.
"Some of the jars are over 2 meters [6.5 feet] or perhaps even 3 meters [10 feet] in height, and in girth you couldn't get your arms around most of them," O'Reilly said. "And there are variations in the design of the jars: some have larger or smaller openings, some are rectangular, some circular or oval — in some cases you wonder how did they even carve these things?"
The variety of sizes and shapes of the jars has prompted many researchers to theorize about their purpose over the years.
"It’s probably likely that they do represent a memorial of some kind, and the variations in the sizes of the jars may indicate that there were differences in status and perhaps a hierarchy in the society that created the jars," O'Reilly said. "You could spend a lot of time theorizing."
Unearthing new mysteries
The burial site with the oddly shaped quartz stone was one of three distinct types of burial sites found at Jar Site 1, the researchers said. [Top 10 Weird Ways We Deal With the Dead]
"This is the first time that this type of interment has been uncovered at the Plain of Jars, but if there is one, there will probably be others," O'Reilly said. "And this burial is also quite interesting because it contained the remains of not one but two individuals: the cranial bones of what's estimated to be an 8-year-old child were found in that burial as well [as an adult skeleton]."
The expedition also uncovered 11 ceramic jars, which are expected to contain "secondary" burials of human bones from which the flesh was removed. A pit filled with bones from several secondary burials and covered with a large limestone block was also found, and the marker stones and stone disks on the ground around the stone jars seemed to correspond to the location of secondary burials, O'Reilly said.
Scientific study of samples and remains from the Plain of Jars site will continue in the laboratory. O’Reilly said the expedition recovered some human teeth that could provide DNA for testing and clues to the origins of the ancient peoples buried there. But, DNA tends to degrade heavily in the climate conditions of Southeast Asia, so a proper analysis might not be possible, he added. The contents of the ceramic jars excavated from the site will also be carefully examined to confirm if, as the researchers suspect, they hold human remains.
But the Plain of Jars is not giving up all its secrets just yet. Although some archaeologists have proposed that the stone jars were used to decompose bodies before the bones were cleaned for secondary burials, it may be impossible to know for sure.
"This is something you find in various religious practices in different parts of the world, but it's something that needs to be investigated a little further at the Plain of Jars," O’Reilly said.
One of the biggest problems at the site is that the jars have been exposed to the harsh Southeast Asian climate for more than 2,000 years, making it very difficult for scientists to study and run test on the artifacts.
"Possibly we could look at trying to extract lipids from the stone jars to see if there is any evidence for decomposition of human remains, but the jars have been exposed for so long that it's a bit of a long shot," he said. "So, I fear we probably will never know the true purpose of the large stone jars."
Sign up for the Live Science daily newsletter now
Get the world’s most fascinating discoveries delivered straight to your inbox.
Tom Metcalfe is a freelance journalist and regular Live Science contributor who is based in London in the United Kingdom. Tom writes mainly about science, space, archaeology, the Earth and the oceans. He has also written for the BBC, NBC News, National Geographic, Scientific American, Air & Space, and many others.