Placed on rocky ledges throughout the Cardamoms, hundreds of metres above sea level, are some 70 ceramic jars, hundreds of years old. Inside them: the bones of around 150 people who sheltered in the jungle during the decline of Angkor. New theories have emerged about who they were, and what their relationship was with their aggressive lowland neighbours. Poppy McPherson reports.

A couple of weeks ago, Dr Nancy Beavan discovered the strangest thing. People who know her would not be surprised, as discovering strange things is something of a specialty of hers.

The 56-year-old American, an expert in radiocarbon dating, has spent the past decade pursuing the mystery of some 70 ceramic jars, many containing human and animal remains, found neatly placed on remote ledges throughout the Cardamom Mountains.

She and her research team have found 10 distinct sites so far, but more are now thought to exist, including at least one in the Stung Cheay Areng valley area in Koh Kong where environmental campaigners hope the finding might help them protect the area from a destructive dam project.

The jars date back to between 1395 and 1650AD. The 15th century saw the decline of Angkor as the capital of the Khmer empire and the shift of power to new Mekong trade ports such as Phnom Penh. Beavan’s team think the jars could hold vital clues about the era.

The work, for the most part funded on a shoestring, has taken Beavan to some surprising places. Some of the sites are so remote helicopters were required to ferry in food, water and staff for each mission. Others are a little too close to the natural world: she’s woken in the middle of the night to a female elephant plundering the camp – “you could hear her going through the bamboo and the bamboo was just exploding – they never let the fires go down after that.”

When we spoke in Phnom Penh, where she has made her home after years of flying back and forth from the States, she enthused about the findings from her January visit to the largest site, Phnom Khnang Peung, where some 152 people are buried - and some of the bodies show the earliest evidence of scurvy in Southeast Asia [a paper is forthcoming.]

But, in the strangest twist so far, a descendant of the people in the burial jars, who practiced this funeral rite with no precedent in Khmer history, had been working at her side all along.

It started, like most things in her line of work, with some bones.

Centuries before their remote peaks served as a jungle hideaway for the Khmer Rouge, the Cardamom Mountains sheltered groups who opted out of the activities of the lowlands in the Angkorian and post-Angkorian periods.

One of those groups was the Chong people, who were sometimes captured as slaves by the aggressive Angkorian civilisation.

“If you go to the Record of Cambodia by Zhou Daguan, written in the 13th century, he mentions how those people in the hills were thought of as dark and ignorant; and there is a word he uses “tchoung” , I think, and one translation of that is slave,” said Beavan.

One of Beavan’s tentative theories is that the people found in the jars could be from this ethnic group, among others, and that the descendents still living in the Cardamoms could provide clues about the history.

“We are beginning to suspect that perhaps we should concentrate on the Chong, in particular,” said Beavan.

It wasn’t until 2008, when her project was fully underway, that she could get an idea of what the people who were buried in the jars looked like, based on their skeletons from one of the sites.

In 2003, two entire jars, with all the bones in them, were taken from there during the filming of a National Geographic documentary – much to the chagrin of Beavan, who stresses the importance of conserving the sites. The jars are now in the National Museum.

“They were beautiful, beautiful skulls and I thought, ‘Oh my god, I want to see your face,’” she said,

Luckily, she had a friend: Harvey Pratt, a forensic artist who did victim reconstruction at the Oklahoma Bureau of Investigation. An internet search reveals him to be one of America’s best regarded. He agreed to do the work.

“So we did all the measurements, sent all the pictures and he did a facial reconstruction for me, so we got a possible picture of the face of the body jars.”

The sketch revealed a masculine, heart-shaped face with high, wide cheekbones and a toothy smile.

Drawing in hand, she went to visit a village near to Phnom Pel, one of the burial sites, where one of her team, a local guide working in the forest known as Mr Kan, was on duty.

“I’m sitting in front of the ecotourism office and I look up and walking down the street is the face of the body jars. ‘Oh, who’s that?’ ‘Oh, that is forest man.’ ‘No, no, who is that?’ And it turned out to be Mr Kan.”

He had the same striking features and eyes, she said.

“It’s only in the past couple of weeks that we discovered that Mr Kan is actually Chong. Why? Because we’ve been so busy working with him that we never bothered to ask the question.”

A further, even more intriguing theory of a connection between the highlanders and the lowlands arose when the team noticed a similarity between each of the sites.

The vast majority of the jars are mae nam noi storage jars, around 50cm tall and believed to have been made in kilns along Thailand’s Chao Phraya River, which played a major part in the maritime trade cargoes of ships plying the Gulf of Thailand from at least the 14th century.

According to Tep Sokha, Beavan’s research partner and an expert in Cambodian ceramics, they also found bowls and plates made by Thai potters at the largest Phnom Khnang Peung site.

“They may have been used for food offerings, when highland people made funereal rituals by practicing jar burials,” he said.

However, at every single site, there is one Angkorian jar among the others. At Phnom Khnang Peung there were three, two of which had burials inside.

“The use of this jar might be indicative of yet another kind of relationship,” said Beavan.

“Our supposition was that these people had no association with Angkor. During that time, people of the highlands were considered Chong slaves.”

Her curiosity was piqued.

Another academic, Roland Fletcher, Professor of Archaeology at the University of Sydney, pointed towards a 2004 paper by the historian Michael Vickery. In it, Vickery discusses references in ancient texts to the last king of Angkor, Ponhea Yat.

He cites texts claiming that Yat persuaded certain groups to rebel against the Ayutthayans who were controlling Angkor for a short time in the 1430s and 40s, and was eventually captured.

After escaping, he is believed to have taken refuge with the barrg people, a term to describe the ethnic groups living “somewhere in western Cambodia or the adjoining provinces of Thailand”, according to Vickery, and encompasses the Chong.

According to Vickery, Yat was the son of a deposed Ayutthayan king exiled to Cambodia, who married into the non-Khmer population of the western borderlands who were later Yat’s allies.

Beavan believes the Angkorian jars could be a reference to some of the people in the highlands having had a relationship with him, and his political machinations.

“There’s really not a good idea about who the barrg were, but they might have been highlanders,” said Beavan, adding that there are many historical references to people going to the highlands to muster armies.

“As any tentative idea, and lacking something like a signed pay receipt from Yat among the jar burials, the relationship certainly can’t be proven. What I am doing at the moment is the radiocarbon dating on the bodies that were buried inside the Angkorian jars at Phnom Khnang Peung.”

Even if she gets radiocarbon ages between the 1430s to 1463 (the beginning of Yat’s involvement in the revolts, to his death), the dates will not prove the connection to Yat, though she hopes ethnographic interviews later this year with the current inhabitants may bring her closer to the truth.

The reason for exploring the idea was due to the difference in the distribution of Angkorian jars in the Cardamoms as compared to other highland areas.

People living in upland areas of Southeast Asia that encompasses central Vietnam, north east Cambodia, and southern Laos have long used jars to ferment rice beer, incorporating them into burials, and handing them down as family wealth.

“The people who created the Cardamom burials are hardly alone in this,” said Louise Cort, the Curator for Ceramics at the Freer Gallery for Art and Arthur M. Sackler Gallery, Smithsonian Institution in an email from Kyoto.

What is new, however, is the burial in rock shelters. “In the Vietnamese central highlands, different burial practices are followed, although they also involve jars,” she added.

“Secondary burials, in which the bones are reburied, is a widespread practice, but clearly it takes many forms in the details of how it is carried out.”

For Beavan, the Cardamom people differ “because their Angkorian jars sort of stick out like a sore thumb among the large collections of mae nam moi. Why, if you are collecting mae nam moi with such a passion, do you pop in one Angkorian jar? What does that mean?”

Beavan, and Sokha believe it is people like Mr Kan who might know the answer.

Local people have been found to make visits to the sites.

At some, the team found little plastic bags where a food offering had been left within recent months.

On one occasion, they encountered a group of 17 people from the village below who had walked for miles and stayed two nights and three days in the forest – a “pilgrimage”, Beavan said.

In October, they will travel to Stung Areng, one of several places home to Chong people, including Pursat and Pailin.

“There will be stories that we can collect from the older people, but, wow, if those same questions had been asked back in the 1930s or something, it would have been great.”

Some of those stories have already hinted at the existence of new sites, known only to a few local villagers.

At least one of those is believed to be in the Stung Areng valley area, where monks at a local temple have led a drive to protect the area and halt the progress of a Chinese dam project expected to flood thousands of hectares of protected forest.

“There’s been rumour after rumour,” said activist Alejandro Gonzalez-Davidson, who has been working with the local community for 10 years, speaking from Koh Kong City the day before a planned one-day trek to one of the apparent sites

“A few sites there are known to a few villagers but not to the outside world,” adding that if they turned out to be authentic, it would be a “big pull” for visitors, and could aid the attempt to preserve the area as an ecotourism site.

Does Beavan think there is a real possibility these jars could fit the pattern of the other sites she has seen?

“Yes, I do. The known sites form a sort of linear pattern from north to south along that ridge line of the eastern Cardamoms; but there is a big gap between the Khnorng Sroal site and the northernmost site, Khnang Tathan. I think there is a very good possibility of previously unknown sites in that Areng area.”

“The potential for ecotourism in that area is very high,” she added. “I think this has been previously shown by other successful community-based ecotourism projects, such as the Chi Phat community’s, which combines wildlife tours, hiking, bike trials, and, of course, visits to the heritage site Phnom Pel with its jar and coffin burials.”

Whether or not Stung Areng’s sites are authentic, one thing is certain: Beavan will find out.

That’s the lesson learned from Mr Kan – “the greatest example of, ‘oh, duh!’” for the researcher. She and Sokha plan to take Gan to Stung Areng – where his family originally came from.

“That’s the interesting thing about research. You can have a research plan, but unless you stay open-minded and wondrous, you might miss something.”