Life in high-altitude mountains can be rough. Resources are scarce, the weather can be extreme and oxygen levels hover at dangerously low levels. Archaeologists have thus assumed that towering mountains and plateaus were among the last places to be populated by ancient humans. But a new study suggests that this assumption could be wrong.

Published in the journal Science, the research details a remarkable discovery in Ethiopia’s Bale Mountains at a site located more than 11,000 feet above sea level. There, a team of experts unearthed a trove of artifacts—among them stone tools, clay fragments, burnt animal bones and a glass bead—indicating that people had lived there as early as 47,000 years ago. These finds, according to the study, represent “the earliest evidence of a prehistoric high-altitude [human] residential site.”

For decades, paleoanthropologists working in east Africa have been concentrating their attention on lower-altitude locations. “We were simply the first to go higher,” Götz Ossendorf, an archaeologist at the University of Cologne and lead author of the new study, tells Carl Zimmer of the New York Times. But reaching Fincha Habera, as the site of the new discovery is known, was no mean feat. The research team had to trek more than 700 miles on foot and by pack horse to get to the site.

The effort was worth it. At Fincha Havera—one of more than 300 elevated rock shelters that the researchers investigated—they quickly dug up signs of ancient human occupation. Crucial to their discovery were the remnants of hearths, which provided charcoal that could be dated to between 47,000 and 31,000 years ago, according to Zimmer.

The new findings are not, however, the first clue that our ancestors ventured to high altitudes earlier than experts once thought. Earlier this year, for instance, scientists reported the jawbone of a Denisovan—an extinct hominin species—that was discovered in a cave some 10,700 feet above sea level in China. The specimen was dated to around 160,000 years ago. Also significant was the discovery of stone tools high on the Tibetan Plateau, with the relics dating between 30 and 40 thousand years ago. But the Fincha Habera finds offer unusually robust evidence of humans actually living at high altitudes.

The settlement was probably not a permanent one. “Prehistoric humans at that time were mobile hunter-gatherers, so they never stayed sedentary at a single site,” Ossendorf tells Charles Q. Choi of Live Science. But, Ossendorf notes, the evidence suggests that prehistoric people “spent considerable amounts of time” at the site. In fact, Fincha Havera was repeatedly populated by humans; the team’s analysis shows that around 10,000 years ago, a second group moved into the site, increasingly using it as a hearth.

In spite of the challenges of high-altitude living, Fincha Havera’s ancient occupants may have seen it as prime real estate. They inhabited the site during the Last Glacial Maximum, when much of the Bale Mountains were covered with ice—but Fincha Havera was located beyond the icy region. Melting glaciers would have offered an ample supply of water, perhaps more than could have been found in lower—and drier—valleys. Food seems to have been plentiful at Fincha Havera, as the researchers found “abundant burnt bones, mostly of giant mole-rats,” the study authors write, suggesting the site’s inhabitants were roasting rodents for meals. They also seemed to have been using nearby obsidian outcrops to make their tools.

"The settlement was therefore not only comparatively habitable, but also practical,” says Bruno Glaser, study coauthor and expert in soil biogeochemistry at the Martin Luther University of Halle-Wittenberg in Germany.

The researchers plan to return to Fincha Havera for additional excavations, according to Zimmer. Ideally, they would like to find the bones of the humans who lived there—even more ideally, bones with extractable DNA. Such a find could help scientists learn more about how ancient humans adapted to high altitudes and whether those adaptations have been inherited by mountain-dwelling peoples of the present day.