Discovering the ancient stone jars of Laos ... and their creepy secret

In the quiet valleys and grasslands of northern Laos, thousands of enormous stone jars have marked the landscape for millennia. The ancient people who put them here and what they were used for have long been a mystery - but just last month, an Australian archaeologist announced he had discovered an answer. And it's creepier than we could ever have imagined.

When I visited the Plain of Jars last year, the mysteries of these ancient stones were part of the appeal. It was a long trip to get there - starting with a bumpy journey in a minibus from the busy tourist city of Luang Prabang to the decidedly non-touristy city of Phonsavan. There were moments I wondered if the road had been built at the same time as the jars, it was in such disrepair. To cover the 250 kilometres, it took about 10 hours.

Eventually arriving in Phonsavan as the sun set, I found a local guide called Kongkeo who agreed to take me to the archaeological areas the next day. Although the name people use - the Plain of Jars - implies visiting a single location, there are actually more than 100 distinct sites scattered across the region, containing anywhere from a handful of the stone monuments to hundreds. For tourists, there are three main places that are worth going to.

Kongkeo drove us to the first location, unimaginatively called Site 1. "Most of the sites are found on hill slopes and ridges," he explained, "but Site 1 is on a plain, which is where the Plain of Jars name comes from." Here, across the open grasslands, I could immediately see the hulking vessels positioned randomly every few metres or so - almost like gravestones in a cemetery but without strict rows or regular spacing.

There's no consistent sizing to the jars, but many are as tall as a human - and several times wider. These stout pieces have not been moulded like pottery. They are huge chunks of stone that have been carved to hollow out the interior and give the exterior a cylindrical form. I pulled myself up and over the edge of one of the largest ones, looking down into its well-like centre. I could easily fit inside.

It's this person-ish size that has led researchers from initial theories that the jars held water and food to the assumption they were actually for funerals or burials, Kongkeo told me. We don't know much about the Iron Age civilisation that sculpted them between 500 BC and 500 AD, but some of their human remains have been found here, along with glass beads possibly used for the decoration of bodies. In a cave on the edge of the plain, Kongkeo pointed around, explaining it may have been the crematorium for Site 1.

But for decades, theories were all we had. Which is why I was so intrigued to see the recent news that the mystery of these jars may have been solved (at least, some of it). In findings published in the journal Antiquity, Nicholas Skopal from James Cook University revealed his team had made an incredible discovery at a location called Site 75. Inside just one large jar, they found bones from at least 37 people. But most fascinating was the way the remains had been arranged to use the space efficiently - skulls were stacked around the rim, with thigh bones laid across the edges. Not all body parts were included, but there were iron tools, pottery and a copper bell. Essentially, this jar was a miniature ossuary for an entire family or community!

The finding "significantly improves our understanding of the antiquity of megalithic jars in Southeast Asia," Skopal says. But why did it take so long? I discovered part of the answer when Kongkeo stopped at a small museum in Phonsavan to show me the piles of rusting ordnance collected since the US bombing campaigns here in the early 1970s. More than two million tons of explosives were dropped on Laos during the Second Indochina War but about a third of cluster bombs didn't detonate. Many are still lying amongst the jars and could go off if disturbed. It's too dangerous to visit the majority of the jar sites, so they remain closed... even to professional archaeologists.

"Although it's been 50 years, we still feel like the war hasn't ended because there are bombs everywhere," Kongkeo told me.

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There is still lots of work for researchers to do here, including working out the different uses for the various sizes of jars - perhaps bodies decomposed individually in smaller ones before bones were transferred to the larger group tombs, for instance. But that may not be a bad thing, because a bit of mystery adds to the fun of exploring an ancient landscape like the Plain of Jars.

Laos still gets much fewer visitors than its Southeast Asian neighbours of Thailand and Vietnam. Those tourists who do come tend to focus on places like Luang Prabang. But the good news is that the road to Phonsavan is much better if you come the other direction from Vientiane. And now, with this new discovery, the story of the Plain of Jars is also more accessible.