Deep inside the Bruniquel Cave in France, a set of man-made structures 336 meters from the entrance lie as evidence to the former populations which inhabited the cave. These are among the oldest structures created by humans, and they have quite a story to tell about some of our ancestors. Until now, the earliest dated structures go back to only 38,000 years — found at Chauvet, also in France — but these structures were dated back to 176,500 ago.

Measurements for the archaeo- magnetic study in Bruniquel cave.
© Etienne FABRE – SSAC.

A unique cave

Bruniquel is a tiny village in the Midi-Pyrénées region in southern France, known for its nearby system of caves, most notably the Bruniquel cave. Bruniquel Cave was discovered in 1990 on a site overlooking the Aveyron Valley, and since then, the speologists and archaeologists working in the area have maintained the cave in pristine shape – and it’s a great thing they did so.

The cave itself is a wonder, and unique. It features numerous natural formations (an underground lake, calcite rafts, translucent flowstone, concretions of all types, etc) as well as intact floors containing numerous bone remains and dozens of bear hibernation hollows with impressive claw marks. But without a doubt, the most important feature of the cave is a system of almost 400 structures, stalagmites or sections of stalagmites, gathered and arranged in more or less circular formations.

“There are no comparable known structures. The structure of Bruniquel is unique. There are other sites, at the surface of similar or older age with some traces of constructions, but they are much less preserved, nothing to do with the Bruniquel structure,” Sophie Verheyden of Royal Belgian Institute of Natural Sciences, Brussels told ZME Science.

These stalagmites bear obvious signs of fire use. Hundreds of meters into the cave, in almost complete darkness, the cave’s inhabitants made fire. We know this because the calcite in the formations was reddened or blackened by soot, and in some places it was even fractured by the heat. There is also plenty of burnt matter, including some burned bones which were carbon dated to 47,600 years – this being the oldest possible date using that technique.

But after this analysis in 1995, no further studies were carried out until 2013.

3D reconstruction of structures of the Bruniquel cave.
© Xavier MUTH

In 2013, a team from the DRAC Midi Pyrénées regional archaeological department launched a new program of studies. They developed a thorough inventory of all the available cave formations and artifacts, weighing an estimated 2.2 metric tons. Additionally, they carried our 3D surveys of the stalagmite structures and a magnetic study which reveals the anomalies caused by heat making it possible to map the burnt remnants found in this part of the cave. But the problem of dating still remained.

Close-up of fire traces with « speleofacts » in the Bruniquel cave.
© Michel SOULIER – SSAC.

In order to bypass this issue, they employed an uncommon technique in archaeology: uranium-thorium series dating (U-Th). When stalagmites are formed, uranium is present in the calcite. But as time passes, the uranium breaks down into other elements, including thorium. By mapping the uranium-thorium (U/Th) ratio, the age can be determined and this method can go way longer than carbon dating, though with a lower accuracy. Much to the surprise of researchers, the age came out at an astonishing 175,000 years ago – plus minus 2,000 years ago, but it’s still several times older than the previous record.

Neanderthals were the first explorers and builders

The very existence of these structures at such an old date is spectacular. The earlier examples of man-made structures date from 36,000 years ago (Chauvet) and 22,000 years ago (Lascaux) – Bruniquel is older by almost an order of magnitude. But it gets even better.

The Bruniquel stalagmite structures were built long before modern humans arrived in Europe (-40,000 years). This means that they must have been built by Neanderthals, 100,000 years before humans even got there. Most anthropologists believe that Neanderthals didn’t venture too much in caves, and didn’t have the sophistication necessary to make fires so deep in caves, were there’s little to no light. But this raises even more questions.

“The future research will concentrate on an even more detailed study of the structure and the different pieces, on the entrance of the cave (how did these people enter the cave? where is the exact entrance at that time, when was it naturally closed?) and on the synchronous or not entering of bears and humans,” Verheyden added in an email.

OK, so the Neanderthals were bright enough to make fire and structures, but why did they do it? It doesn’t make much sense to build a shelter so deep in the cave, so they likely had a different purpose. Possible options include water storage or cultural/religious purposes. But if the Neanderthals were so advanced, we might just have to rethink what we know about them.