What modern-day researchers don’t know about Neanderthal culture could—and does—fill many books. After all, it’s not exactly easy to reconstruct cultural practices of a human subspecies that lived hundreds of thousands of years ago and didn’t leave much behind. Now, there’s another entry for the books: Researchers have determined that stalagmite walls in a French cave were built by Neanderthals for mysterious purposes.
In a paper published in the journal Nature, the team describes their quest to examine and date a group of strange structures inside Bruniquel Cave in southern France. Thousands of years ago, the cave's entrance collapsed, closing it off for exploration until local speleologists discovered it in 1990. Inside, they found multiple semicircular walls made of broken-off stalagmites. There were no footprints inside the cave, but there was a burnt bone nearby that turned out to be so old its age couldn’t be confirmed by carbon dating, which is only accurate for objects up to 50,000 years old.
Archaeologist François Rouzaud wondered if the stalagmite structures had been built by Neanderthals, but soon after he began his investigation tragedy struck. He was killed while leading an expedition in another French cave and the investigation foundered. Until another researcher took up the project, that is. As Ewen Callaway reports for Nature, paleoclimatologist Sophie Verheyden ended up moving nearby and became intrigued by the cave. She assembled her own team and decided to investigate.
What they found is even more enigmatic than the stacked stalagmites themselves: traces of fires within the semicircles. Uranium dating revealed that the stalagmites were stacked around 175,000 years ago, which puts them among the oldest structures ever constructed by a human relative.
There’s just one problem: Nobody is sure exactly what the hearth-like structures were used for. In their paper, the team writes that they could have been used for ritual purposes—or just to keep Neanderthals warm.
Of those possibilities, ritual uses are the most intriguing. That explanation would fit in with what scientists already know about Neanderthals, who were smart enough to build their own tools and even bury their dead. The stalagmite structures may be a mystery wrapped in an enigma, but just knowing they were built by Neanderthals gives a new appreciation for the brains—and building savvy—of that long-gone group.