Once it was thought hardly anyone ventured into the Amazon before Europeans arrived in South America, instead keeping close to major rivers. But that was before satellites combed the region. Archaeologists at the University of Exeter who surveyed satellite images in areas of deforestation have uncovered 81 previously unknown Amazon settlements—some covering hectares, others as small as 100 feet wide—marked by fortification ditches, sunken roads, ceramic fragments, and earth platforms on which wooden houses would've stood between 1250 and 1500, reports the Guardian. "We filled the last piece of a puzzle in Amazonian archaeology," study author Jonas Gregorio de Souza tells Live Science, describing a network of settlements believed to have covered 154,000 square miles of the Amazon's southern rim, perhaps supporting a population in the millions in the pre-Columbian era.
Archaeologists couldn't get access to all 81 sites in the upper Tapajós Basin, but examined 24 in person and believe hundreds more exist. In addition to upending the idea that the Amazon was mostly untouched, their study in Nature Communications "definitively discredits early low estimates of 1.5-2 million inhabitants for the whole basin," they say, per USA Today, and shows settlements next to small streams and springs may have hosted large populations. Though linked to other settlements, the sites each have "a different local expression of … architectural traditions," says de Souza. "There are different kinds of site layouts and artifacts that are found in each of the regions." De Souza adds many questions remain, but "the big debate is how populations were distributed." Scientists expect to learn more as additional sites are discovered and examined. (Stonehenge-like structures were also found in the Amazon.)