175,000-Year-Old Underground Circles Built by Neanderthals

Neanderthal's face.

The finding of 175,000-year-old structures deep inside a cave in France suggests that Neanderthals ventured underground and were responsible for some of the earliest constructions made by hominins. (Image: via Natural History Museum, London)

All too often, Neanderthals are seen as thick-browed thugs. As recently as the late 1990s and early 2000s, the mainstream scientific community simply rejected the idea that Neanderthals were intelligent or sophisticated. Over the years, after their discovery, scientists have tried to understand why Neanderthals died out and we survived, with the assumption that they were inferior in some way.

However, our human relatives were immensely capable, with evidence of stone tools and other artifacts Neanderthals left behind. The Neanderthals had harnessed fire, lived in shelters, wore clothes, and mastered the art of stone tool making. It is understood by some researchers that Neanderthals even buried their dead, adorning the graves with flowers.

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The discovery of the cave

In 1987, Bruno Kowalsczewski and his father noticed faint wisps of air emerging from an ancient rock slide. Bruno, a young caver aged 15 at the time, knew that this may be the entrance to a cave. He spent three years clearing away the rubble, and finally dug out a tight passage measuring 98 feet (30 m) long — large enough to enter the cave. For the first time in tens of thousands of years, the Bruniquel Cave in France’s scenic Aveyron Valley was about to have the echo of human footsteps through its chambers again.

As Bruno and members of the local caving club entered the cave, they found themselves in a large, roomy corridor. The floor was covered by pools of water, and the walls were scattered with stalactites and stalagmites. The cavers could also see animal bones scatted around and signs of bear activity; however, none of these seemed recent. They continued down the cave with their torchlight shining their way. Then, around 336 meters into the cave, they stumbled across something that was just extraordinary.

The cave opened up into a huge chamber, where the caver’s lights revealed several stalagmites that had been deliberately broken. As their light moved across the chamber, the cavers soon discovered six structures made from around 400 pieces of broken stalagmites with a combined weight of about 2 tonnes. Two of the structures were comprised of two rings, with one ring measuring between 4 and 7 meters across, and the other one smaller at just 2 meters wide.

While some broken pieces of stalagmites were placed against these rings, others had been stacked into four piles. As the cavers searched around more, it became obvious these weren’t natural formations. Then, when they discovered traces of fire everywhere and a mass of burnt bones, the cavers were convinced this wasn’t the work of bears, but that they were built by people.

Two mysterious stone rings found deep inside a French cave were probably built by Neanderthals about 175,000 years ago, proving that the ancient cousins of humans were capable of more complex behavior than previously thought, scientists say.
Two mysterious stone rings found deep inside a French cave were probably built by Neanderthals about 175,000 years ago, proving that the ancient cousins of humans were capable of more complex behavior than previously thought, scientists say. (Image: Etienne Fabre via SSAC)

Archaeologist Francois Rouzaud

Bruno soon recognized the significance of the site and called archaeologist Francois Rouzaud. Carbon-dating was conducted on a piece of a burnt bear bone found within the chamber; however, no radioactive carbon was left in it, suggesting the bone was older than 50,000 years, which is the limit of carbon dating.

If this result was right, it would mean that the stalagmite rings were older than any known cave painting. It also proves that it wasn’t the work of Homo sapiens, leaving the only early humans in the area at the time, Neanderthals. The discovery also shows that Neanderthals employed fire to venture deep underground, and were capable of shaping the subterranean rock into complex constructions. This also shows Neanderthals were much more sophisticated than science has given them credit for.

The most prominent formations were the two ringed walls that were built four layers deep in places. Stalagmites were wedged in place as vertical stays to help support the layers, which, in some areas, stood up to 19 inches (50 cm) high. The site had round holes in the ground where the stalagmites once stood before being pulled from the cave floor. Blackened and reddened stalagmites, which were fractured from heat, showed clear signs of fire damage, indicating the fire was used for lighting.

Rouzaud had plans to investigate Bruniquel Cave further, however, while guiding colleagues through a different cave in 1999, he suffered a fatal heart attack. Following his death, access to Bruniquel cave was restricted, leaving its incredible contents in the dark for a further 14 years.

Curiosity reopens the cave

Palaeoclimatologist Sophie Verheyden from the Royal Belgian Institute of Natural Sciences in Brussels, and a keen caver, became curious about the cave after buying a holiday home nearby. It wasn’t long before she gathered a team of archaeologists and geochronologists — among other experts — to explore the mysterious structures themselves.

Verheyden suspected that Rouzaud’s date of 47,600 years may not be telling the whole story as the date was right at the carbon-dating technique’s limits of 50,000 years. Because she specializes in stalagmites, her first thought was: “Why hadn’t anyone dated the broken stalagmites themselves?” They very well could be much older.

In 2013, Verheyden gained permission to crawl into the mysterious cave to study the site. Her team, which included archaeologist Jacques Jaubert and fellow stalagmite expert Dominique Genty, then started their journey into the dark cave. Verheyden described how it wasn’t a walk in the park: “I’m not very big, and I had to put one arm before me and one behind to get through. It’s kind of magical, even without the structures.”

Neanderthal cave with stalagmites.
The ringed walls are made from nearly 400 stalagmites that have been pulled from the ground and stacked on top of one another. (Image: Michel Soulier via SSAC)

A reassessment of evidence from Bruniquel cave

Verheyden took core samples by drilling into the stalagmites; observation of the core samples showed an obvious transition between the two layers. One layer consisted of older minerals that indicated the original stalagmites; the other layer showed fresher minerals, which had been laid down after the fragments were broken off.

By measuring the uranium levels of each layer the team was able to accurately tell when each stalagmite had been snapped off. The results — the structures were made 174,400 to 178,600 years ago, revealing what Verheyden had suspected — the simple walls were much older than thought. This makes it one of the world’s oldest constructions.

More than 120 fragments had signs of burning, suggesting fires were made within the walls. Dominique Genty, a geoscientist at the Institute Pierre-Simon Laplace in Gif-sur-Yvette who co-led the study, said in a statement: “It’s obvious when you see it, that it’s not natural.” While evidence of bears was found in the cave, which consisted of claw marks, paw prints, tufts of fur, and even hibernation holes, they were not able to stack stalagmites into foot-high walls.

Knowing that the construction predates the arrival of modern humans in Europe, it only leaves Neanderthals, who were the only hominins in the region. The authors of the study wrote: “The Neanderthal group responsible for these constructions had a level of social organization that was more complex than previously thought.”

What makes the site even more remarkable is how well preserved it is. This was due to the stalagmites becoming encased in calcium carbonate soon after the walls were built. Had the site been made closer to the entrance, it would have most likely weathered away during the 175,000 years before its discovery.

So far, there have been no remains of early humans, stone tools, or other signs of occupation found. However, the researchers believe the inhabitants of the cave may have left items behind, but now they may be covered in thick calcite. Jacques Jaubert, a professor of prehistory at the University of Bordeaux, and co-author explained that it’s likely the objects would have been: “Covered with thick calcite, leaving them frozen for eternity, time will tell if future excavations within the cave can recover additional artifacts.”

What was it used for?

While the true reason the Neanderthals used this remains far from clear, the team speculates that the purpose could range from spiritual to more domestic use. However, Harold Dibble, an archaeologist at the University of Pennsylvania in Philadelphia, said: “Constructing some sort of structure — things a lot of animals do, including chimps — and equating that with modern cultural behavior is quite a leap.”

Marie Soressi, an archaeologist at the Leiden University in the Netherlands, wrote a News and Views article for Nature that accompanies the report: “That it is no surprise that Neanderthals living 176,000 years ago had the brains to stack stalagmites. They made complex stone tools and even used fire to forge specialized glues. I think we have several lines of evidence showing that the cognitive abilities and behaviors of Neanderthals were complex. More surprising is the revelation that some ventured into deep, dark spaces. I would not have expected that, and I think it immediately changes the way we are going to investigate the underground in the future.”

As it stands, all options should remain open as it’s not even certain the walls were even made for a specific purpose. The discovery raises plenty of questions, such as why did Neanderthals go so deep inside the cave. The only thing for sure is that the structures were built in the dark under challenging conditions, with no natural light to help the Neanderthals.

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