Ancient Amazon: Discovery of 81 New Archaeological Sites Rewrites History of Americas Before Columbus

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This aerial photo shows site ZMt04, which contains the two largest enclosures (360 to 400 yard diameter) identified during the survey. José Iriarte

For a decade, archaeologists have been racing to study deep mysterious trenches slashed through the soil of the Amazon. Rings, squares and hexagons have pointed to long-forgotten human settlements in a region previously neglected by researchers.

Now, the discovery of 81 new archaeological sites has confirmed that up to a million people lived in an area spanning just 7 percent of the basin before the arrival of Europeans.

Old estimates of up to two million inhabitants across the whole of the Amazon need to be thrown out the window, the researchers wrote in a study published in Nature Communications,

Buried Under a Forest Canopy

Archaeologists used to think pre-Columbian human populations were spread out in pockets around the major floodplains of the rainforest. But, recent deforestation has revealed huge geometric shapes in the ground from Bolivia to Brazil.

Vast soil glyphs suggest complex societies that manipulated their land with canals, roads, water reserves, and causeways.

In the present study, researchers used satellite image surveys to search for undiscovered soil glyphs across the Upper Tapajós Basin in Brazil. The team found 104 earthworks in more than 81 new archaeological sites. Descending upon 24, they discovered hard evidence of pre-Columbian human habitation; ceramics, stone axes, fertilized soil known as "dark earth" and even old garbage dumps.

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Large and small, the sites varied from hamlets to complex fortified settlements with multiple mounds, plazas and roads.

Major Settlement Across the Region

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An aerial photo of site Mt05: a circular enclosure (150 yard diameter) located on a hilltop. José Iriarte

Extrapolating from earthwork evidence, the authors estimate that people lived throughout the Southern Rim of the Amazon—a region spanning some 150,000 miles². The total population may have reached somewhere between 500,000 and one million in late pre-Columbian times.

Even at the lower end of the team's estimates, the research "definitively discredits" old estimates of some 1.5 to 2 million inhabitants of the entire basin, authors wrote.

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The research rewrites the history of this part of the Amazon. Humans weren't just sprinkled in small floodplain settlements, but spread across the region. These people had a major impact, quite literally, on the land.

"There is a common misconception that the Amazon is an untouched landscape, home to scattered, nomadic communities. This is not the case," study author Jonas Gregorio de Souza, from the University of Exeter, U.K., said in a statement. "We have found that some populations away from the major rivers are much larger than previously thought, and these people had an impact on the environment which we can still find today."

Understanding the past, the researchers think, will help governments prepare for the future. "An understanding of the historical role of humans in shaping Amazonian landscapes, and to what extent these forests were resilient to historical disturbance is critical to making informed policy decisions on sustainable futures," they wrote in the paper.