From the outside, it looks like countless other rural sites in Europe.

But a new study shows that behind the grass and hills by the River Aveyron in south west France, lie some of the world’s oldest-known man-made constructions.

Deep inside the Bruniquel caves are centuries-old semicircular walls made of some 400 large, broken-off stalagmites.

Enigmatic French cave structures show off Neanderthal skills https://t.co/eqMDgEBtz3pic.twitter.com/GKK1iFBWGB — Reuters Science News (@ReutersScience) May 26, 2016

Analysis of calcite on the stalagmites and stumps enabled a team of scientists to determine that the structures were made between 174,400 and 178,600 years ago.

The six structures provide the best evidence yet that Neanderthals began occupying caves much earlier than initially thought.

In places, the semicircles are up to 6.7-metres wide and the structures making them up all show signs of burning, suggesting fires blazed inside the cave.

There are, so far, no remains or other signs of occupation in the cave. However, prehistorians believe the semicircles must have been made by Neanderthals as there’s no evidence of other humans in western Europe at that time.

Evidence collected about Neanderthals shows they had the brains to make complex tools made of stone and even used fire to forge special glues.