Some 25,000 years ago, prehistoric humans gathered dozens of mammoth bones from the Russian steppes and arranged them in a massive circular structure for reasons that are still mysterious.
The incredible structure is the “oldest known circular mammoth-bone feature built by modern humans on the Russian Plain,” according to a study published on Monday in the journal Antiquity. The gnarly bone circle may have provided shelter, warmth, storage, and ritual significance to this Ice Age community.
This is far from the only bone circle made by ancient peoples—roughly 70 of them have been found strewn across Ukraine and Russia since the 1950s. But the site, which was discovered in 2014, is 3,000 years older than its neighboring circles at Kostenki 11, a major hotspot for archaeologists that lies roughly 300 miles south of Moscow.
“The mammoth-bone circle is large, with a diameter of approximately 12.5 meters (41 feet) and is positioned on an east-facing slope with an incline of approximately six degrees,” said the authors, led by University of Exeter archaeologist Alexander Pryor. “The bones form a continuous circle that has no obvious entrance.”
In an email, Pryor said that it is not yet possible to estimate how many humans occupied the site, but it was likely not a permanent settlement.
“We have just started a second phase of research that aims to shed further light on the activities carried out inside the circle, particularly focusing on the role of food storage at the site,” he said.
“If at least some of the mammoth were hunted, this is going to generate a lot of food from each kill. Therefore, preserving and storing that food could be a really significant part of what humans were doing there.”
These Russian plains are infamous for harsh winters in modern times, so it is mind-boggling that humans clearly persisted there in “a period of intense cold when similar latitudes in Europe were already abandoned in the face of the Last Glacial Maximum,” according to the study.
Pryor and his team were able to extract unprecedented clues about this group’s survival tactics by examining fire pits inside the circle, which indicate that people gathered here to cook meat and burn bones and wood for heat. Indeed, the circle is the first structure of its kind to undergo a systematic “flotation programme,” which is an archaeological technique that can reveal fine details about the materials left by a past community.
The structure is built from more than 100 bones sourced from roughly 60 mammoths, in addition to a smattering of reindeer, fox, horse, and bear remains. Pryor and his colleagues also uncovered signs of knapping, the process by which stones are shaped into tools, indicating that human activity was clustered around the firepits.
The flotation technique revealed that roots and tubers were probably cooked at the site, and that pine and spruce were a major source of firewood for these humans. “The presence of conifer trees near Kostenki—perhaps located in low-lying, moist and sheltered areas in the ravines near to the site—would have been an important resource that attracted hunter-gatherers to the area during the glacial period,” according to the study.
“These trees were perhaps critical to human persistence in this region, while other such areas of Northern Europe were abandoned,” the team said.
Ultimately, archaeologists will need to conduct more research in both the field and the lab to unlock the secrets of these ancient humans. But one thing is obvious right now: These people must have been extraordinarily resilient and resourceful in order to construct such elaborate bone structures in the midst of the frigid Ice Age steppes.
This article originally appeared on VICE US.