Watch: Neanderthals Believed to Have Build These Complex Structures 176,500 Years Ago

Bruniquel Cave is a pitch-black cave with pools of water covering the floor. Stalactites hang down from the ceiling, and none of these features are surprising to find in an inactive subterranean cave. However, what was found in the middle of the cavern floor left experts in awe.

As if building these structures isn't that fascinating for you, experts reveal that the cave has been sealed off and inaccessible to humans for tens of thousands of years. So who broke off and wrestled about 2.4 tons of rock into neat stacks?

Experts who found these mysterious structures in Bruniquel Cave said it has to have been done by Neanderthals, which implies they weren't such simple animals. "Neanderthals were inventive, creative, subtle and complex," study co-author Professor Jacques Jaubert of France's Bordeaux University said. "They were not mere brutes focused on chipping away at flint tools or killing bison for food."

According to ABC News, Neanderthals wrenched fragments of stalagmite from the cave's floor and stacked them into walls, some forming rough circles, and standing up to knee high. Deep inside the cave, more than 300 meters from the entrance, they built six such structure, one almost seven meters wide, tens of thousands of years before the first Homo sapiens arrived in Europe.

The structures are approximately made some 176,500 years ago by firelight, possibly for rituals. It also ranks the French walls among the oldest-known human constructions. According to the multi-national research team, Neanderthals broke stalagmite pillars into about 400 similarly-sized pieces with a total length of 112.4 meters and weighed about 2,000 kilograms. This only meant that Neanderthals knew how to work as a group.

"It adds to the ongoing idea that Neanderthal was more modern than generally thought before," study co-lead author Sophie Verheyden, a geologist at the Royal Belgian Institute of Natural Sciences, tells The Christian Science Monitor in an e-mail. "We never thought he would go so far underground, something that is generally attributed to the modern human" much later.

Because they had already learned how to control fire, some of the stacked stalagmites have burn marks on them and some of the structures appear to be hearths of some sort.

"It's the first really good evidence that we have that Neanderthals penetrated very deep into caves and did something extremely unusual," Michael Bisson, an associate professor of anthropology at McGill University who was not part of the study, tells the Monitor in a phone interview. And, he says, "it's one of the earliest bits of evidence for the structured use of space in the European archeological record."

This suggests that early Neanderthal society was remarkably complex and cooperative, compared to how they were perceived years ago.