Archaeologists discovered 81 earthworks deep in the Amazon rainforest, including fortified villages, roads, plazas, and farms.
The researchers say the region could have supported an interconnected civilization of up to a million people between the years 1250 and 1500.
The Amazon was far more developed before European colonization than archaeologists previously thought.
Deep in the Amazon rainforest, archaeologists found something astonishing: 81 never-before-seen earthworks, which may have supported a complex civilization containing a population of up to a million people.
That's according to new research published on Tuesday in the journal Nature Communications.
Like recent Maya finds in Guatemala's steamy tropical jungle, the settlements were first discovered using satellite imagery, and lidar — a type of radar mounted on low-flying aircraft. Once the sites were spotted, the team verified the findings the old-fashioned way: With boots on the ground.
In the 24 sites the researchers excavated in Brazil's Mato Grasso region — the southern edge of the Amazon where the rainforest gives way to drier savannah — they found evidence of a complicated series of interconnected road networks, farms, and large, fortified villages built on mounds containing defensive ditches, causeways, and plazas.
Some of the geoglyphs, as archaeologists call the sites carved into the Earth, were up to 400 meters across.
During its heyday between the years 1250 and 1500, the researchers calculated that the area could have supported almost a million people. They think there may be hundreds more sites hidden in the jungle in a "continuous string of settlements," Jonas Gregorio de Souza, the paper's lead author, told The Washington Post.
"It seems that it was a mosaic of cultures," de Souza said.
While researchers can't say whether the settlements were united under one state or political entity, the paper's authors write that they likely spoke Arawak languages and shared similar cultural practices.
The Arawak are a group of indigenous people who speak related languages and have populated the region for thousands of years.
The findings subvert the narrative, born during a time when archaeology and anthropology were narrowly focused on Western modes of thought, that complex civilization couldn't have arisen in tropical regions.
While excavating the sites, the researchers found decorated ceramics and bands of dark, nutrient-rich soil — signs that the area was used for intensive farming.
"Many parts of the Americas now thought of as pristine forest are really abandoned gardens," Christopher Fisher, an archaeologist at Colorado State University who was not involved in the study, told The Wall Street Journal.
The Amazon rainforest, once thought of as completely untouched before European colonization except by small bands of hunter-gatherers, may actually have supported a kind of large-scale sustainable agriculture that influences the growth of the forest to this day.
"The forest is an artifact of modification," de Souza, the study's lead author, told The Washington Post. "It has nothing to do with the kind of practice we are seeing nowadays — large-scale, clearing monoculture. These people were combining small-scale agriculture with management of useful tree species. So it was more a sustainable kind of land use."