A 25,000-year-old structure made from the bones of woolly mammoths might have served as a giant food pantry for prehistoric humans.

Eastern Europe is dotted with mammoth-bone rings, which have been interpreted as the remnants of Stone Age dwellings. In 2014, archaeologists discovered one such structure at a Russian site called Kostenki that, at 12.5 metres in diameter, is one of the largest ever found. It was created from the remains of at least 64 mammoths, reports a team led by Alexander Pryor at the University of Exeter, UK. Detailed excavations of the structure suggested that humans burnt wood fires within it.

But the structure held only small quantities of debris from the manufacture of stone tools and almost no animal remains other than those of mammoths — suggesting that humans did not use the structure as a long-term base camp. Its large size would have made it difficult to cover with a roof, say the researchers. They suggest that ancient humans might have used the structure to store food instead.