Hundreds of Mysterious Ancient Earthworks Found in the Amazon

Deforestation has revealed the large geometrical geoglyphs built over 2,000 years ago – their discovery holds valuable lessons for today.

The Amazon rainforest is so rich, so dense with trees, that the forest floor is constantly in the dark. The vegetation hides many things, from isolated indigenous communities who have yet to have contact with the outside world to, as has just been discovered, massive earthworks built over 2,000 years ago.

The ditched enclosures, in Acre state in the western Brazilian Amazon, were discovered during research by Jennifer Watling, currently a post-doctoral researcher at the Museum of Archaeology and Ethnography, University of São Paulo. Hidden for centuries by trees, modern deforestation revealed the 450+ large geometrical geoglyphs.

The earthworks are spread out over roughly 5,000 square miles. And what they were used for is not entirely understood. Few artifacts were found during excavation, leading experts to discount the idea that they could have been villages. Their layout doesn’t indicate they would have been used for defense. They were likely only used on occasion, maybe as ritual gathering spots – but no one can say for sure.

© Jenny Watling

But perhaps even more fascinating is that the discovery flies in the face of the idea that the rainforest ecosystem has previously been untouched by mankind.

“The fact that these sites lay hidden for centuries beneath mature rainforest really challenges the idea that Amazonian forests are ‘pristine ecosystems',” says Watling.

“We immediately wanted to know whether the region was already forested when the geoglyphs were built, and to what extent people impacted the landscape to build these earthworks.”

With a lot of patience as well as state-of-the-art methods, the research team reconstructed 6,000 years of vegetation and fire history around two of the sites. According to University of Exeter, where Watling was earning her PhD during the research, the team found that humans strongly altered bamboo forests for millennia and small, temporary clearings were made to build the geoglyphs:

Instead of burning large tracts of forest – either for geoglyph construction or agricultural practices – people transformed their environment by concentrating on economically valuable tree species such as palms, creating a kind of ‘prehistoric supermarket’ of useful forest products. The team found tantalizing evidence to suggest that the biodiversity of some of Acre’s remaining forests may have a strong legacy of these ancient ‘agroforestry’ practices.

What this suggests is something we’ve seen again and again. People who have lived among certain ecosystems for a long time know how to work with them in a way that sustains, rather than destroys. The coastal areas of British Columbia where First Nations have lived for millennia, come to mind – in 13,000 years of repeated occupation, temperate rainforest productivity there has actually been enhanced, not hampered. It really shouldn’t be so hard.

“Despite the huge number and density of geoglyph sites in the region, we can be certain that Acre’s forests were never cleared as extensively, or for as long, as they have been in recent years,” says Watling.

“Our evidence that Amazonian forests have been managed by indigenous peoples long before European Contact should not be cited as justification for the destructive, unsustainable land-use practiced today," she add. "It should instead serve to highlight the ingenuity of past subsistence regimes that did not lead to forest degradation, and the importance of indigenous knowledge for finding more sustainable land-use alternatives.”