The Amazon May Be Hiding More Than 10,000 Pre-Columbian Structures

Based on a new aerial survey and modeling study, archaeologists suggest at least 90 percent of sites known as earthworks remain undetected

Geometric shapes on green landscape
Researchers have only discovered a small fraction of the pre-Columbian earthworks in the Amazon rainforest, according to new research. Mauricio de Paiva

More than 10,000 undiscovered pre-Columbian structures—and as many as 23,000—are likely hidden beneath the dense foliage of the Amazon rainforest in South America, according to new research.

The Amazon is massive, spanning some 2.3 million square miles across Brazil, Bolivia, Peru, Ecuador, Colombia, Venezuela, Guyana and Suriname. Indigenous societies have lived in the expansive rainforest for more than 12,000 years. But archaeologists have only uncovered a small fraction of their permanent settlements, ceremonial sites and infrastructure.

Now, in a new paper published Thursday in the journal Science, researchers say roughly 90 percent of these sites have yet to be found beneath the canopy.

In a five-year aerial survey, a team of researchers studied a roughly 2,000-square-mile area of the Amazon using lidar, a remote sensing technology that can produce highly detailed, three-dimensional images of the landscape.

They uncovered 24 previously unknown pre-Columbian earthworks, which are intentionally formed elevation changes in the land. These sites, which might include wells, ponds, ring ditches or geoglyphs, could have served a ceremonial, social or defensive purpose, per the paper.

The studied area represents just 0.08 percent of the entire Amazon. So, based on their new finds and the 937 previously discovered earthworks, the team developed a computer model to estimate how many other sites might still be hidden in the rainforest.

Not only did the model consider the land characteristics needed to build the earthworks, but it also took into account the factors that would enable people to survive in a given region. These included the distance from the nearest water source, the amount of rainfall, the temperature and the soil makeup, among others.

Based on those factors, the model suggests between 10,272 and 23,648 earthworks remain undiscovered, with the vast majority of those likely located in the southwestern region of the rainforest.

These predictions wouldn’t have been possible without lidar’s ability to “see” through the Amazon’s dense treetops to the ground below. In the past, researchers identified Amazonian earthworks by using high-resolution satellite data, but that could only work in areas where trees had been cleared.

With lidar, “you no longer have to cut down the forest to know what is underneath it,” writes Juan Miguel Hernández Bonilla for El País.

a square-shaped ditch seen from above with trees and cleared land around it
A pre-Columbian earthwork in the Amazonian landscape Diego Lourenço Gurgel

The new estimate of undiscovered archaeological sites paves the way for future field work in the Amazon. But it may also affect ongoing debates about Indigenous land rights in the region. The earthworks and other archaeological sites serve as “tangible proof of an ancestor’s occupation, way of life and their relationship with the forest,” the researchers write in the paper.

The study also dispels the myth that the Amazon is a “vast, wild expanse” that was shaped only by natural forces, says Takeshi Inomata, an archaeologist at the University of Arizona who was not involved in the project, to Scientific American’s Meghan Bartels. On the contrary, humans left an indelible mark on the environment, the research shows.

Other archaeologists echoed that sentiment, including Michael Heckenberger, an anthropologist at the University of Florida who was not involved in the study.

“There has always been this bias in Western thought that the Amazon was like a Garden of Eden, a primordial society that was inimical to human society,” he tells New Scientist’s Luke Taylor. “We are now seeing there was a significant degree of human intervention and variation just 500 years ago.”

For example, the team discovered high concentrations of 53 domesticated tree species near earthwork sites. These include cacao, Brazil nut, breadnut and Pará rubber trees, plus dozens of others. This demonstrates how the region’s inhabitants altered the natural landscape, likely so they would have a steady supply of food and useful materials.

The Amazon we know today, then, “is a result of the coevolution of Indigenous peoples and a forest over the millennia,” says Eduardo Neves, an archaeologist of the University of São Paulo in Brazil who was not involved in study, to Science’s Rodrigo Pérez Ortega.

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