A region of the Amazon once thought to be devoid of human life may have actually supported a population of up to one million individuals.

The conventional image of the pre-Columbian Amazon basin as a dense, unwelcoming jungle with only a few scattered indigenous tribes along the rivers may need to be revised. Research published in Nature Communications suggests that the rainforest was home to many more people before Spanish colonization than was previously thought.

The Amazon, the world's largest rainforest, poses significant challenges for archaeologists studying its past inhabitants. It was long believed that indigenous Amazonians steered clear of the forest's interior, instead living as nomads along the major rivers. Earlier estimates suggested the entire population of the basin was between 1.5 and 2 million people.

Thanks to satellite technology, researchers are now able to locate remnants of long-forgotten settlements in remote areas of Brazil, without the need to physically explore the jungle. A team of archaeologists from the University of Exeter used satellite imaging to discover geoglyphs—large patterns carved into the earth, likely for ceremonial purposes—in a part of Brazil's Mato Grosso state once thought to be uninhabited.

After identifying the locations of these earthworks, archaeologists traveled to the southern edge of the Amazon to examine them firsthand. At each of the 24 sites they set out to verify, they found actual geoglyphs on the ground. At one site, they uncovered charcoal and pottery dating back to 1410 CE. In total, they recorded 81 new geoglyph sites.

The earthworks would have been carved into the earth during a seasonal drought, allowing the builders to clear a portion of the rainforest. Fortified villages were constructed within or near these glyphs, linked by a network of roads. The researchers used a computer model to estimate that a 154,000-square-mile area could contain the remains of 1,300 geoglyphs and villages, with only two-thirds of them discovered so far. In the late pre-Columbian period, this region, which makes up just 7 percent of the Amazon basin, may have supported a population of 500,000 to 1 million people, according to the researchers' models.

The European invasion brought disease and genocide that wiped out most of these settlements, which were eventually overtaken by the rainforest. However, the remnants of these settlements indicate that deforestation and Amazon development are not new issues.

"Our research shows that the history of the Amazon needs to be reconsidered. It was never just populated along the banks of major rivers, and the people who lived there did indeed alter the landscape," said researcher José Iriarte in a statement. "Studies like ours are gradually helping us assemble a clearer picture of the history of the world's largest rainforest."