A recently published study shows mysterious underground stone structures inside caves in the south of France, and they are said to have been built by Neanderthals.

The structure is made of nearly 400 pieces of stalagmites, which are pillars of mineral deposits that grow upward. They were built about 336 meters from the Bruniquel Cave in southwest France.

According to a report from The Atlantic, the stalagmites had been "deliberately broken" and arranged into two rings - a large one about four to seven meters long, and a smaller one about two meters wide. Scientists also noted traces of fire everywhere and fragments of burnt bones.

According to the study published in the journal Nature, the structure could have been built by the Neanderthals as it seemed to be carefully constructed. "Early Neanderthals were the only human population living in Europe during this period," the report said.

In 1992, 15-year-old Bruno Kowalsczewski discovered the cave for the first time in thousands of years. His father had noticed thin wisps of air escaping through the pile of rocks. It took Bruno three years to clear the rubble and gain access to the cave.

Kowalsczewski brought in archaeologist Francois Rouzaud to study the site, and Rouzaud hypothesized that the Neanderthals were responsible for building the structure. Using carbon-dating, the scientist estimated that the structure was about 47,600 years old, which meant that the rocks were even older than most of the discovered cave paintings.

However, Rouzaud passed away in 1999 before he had a chance to go back to the cave.

This discovery also meant that the structures were not the work of Homo sapiens, rather they were built by the Neanderthals - the only early humans in the south of France during that time.

This early architecture may provide evidence of the unique capabilities of the early human species, and they could have been more than the knuckle-dragging, savage cousins of men.