Ancient people built hundreds of huge, mysterious earthworks in the Amazonian rainforest more than two thousand years ago, transforming the forests in the process.

UK and Brazilian experts have found new evidence in Acre state in the western Brazilian Amazon that sheds some light on how indigenous people lived in the Amazon long before Europeans arrived in the region. Trees concealed the abandoned enclosures for centuries, but modern deforestation has resulted in the uncovering of more than 450 of these large geometrical geoglyphs.

The purpose of these enigmatic sites is still not understood. As very few artifacts were recovered during excavation, they are unlikely to have been villages. The layout also does not suggest that they had been built for defensive purposes. The current thinking among archaeologists is that they were used only infrequently, perhaps as ritual gathering places.

The structures are abandoned enclosures that occupy approximately 13,000 square kilometers. The common belief that the rainforest ecosystem has been untouched by humans is challenged by this discovery.

Jennifer Watling, a post-doctoral researcher at the Museum of Archaeology and Ethnography, University of São Paulo, carried out this research while she was studying for a PhD at the University of Exeter. Dr Watling noted that the idea that Amazonian forests are ‘pristine ecosystems` is strongly challenged by the fact that these sites had been concealed beneath the mature rainforest for centuries.

Watling and her team immediately had two questions when the structures were discovered:

To what extent was the landscape impacted when these earthworks were built? Was the region already forested when the geoglyphs were built?

The team members used state of the art methods and managed to reconstruct 6000 years of fire and vegetation history around two of the geoglyph sites. They found that the clearings that were made to build the geoglyphs were small and temporary, and that bamboo forests were heavily changed by humans for millennia.

The people of that time did not burning large swathes of forest, either for agricultural practices or for geoglyph construction, but rather transformed their environment by concentrating on economically valuable tree species such as palms, and then creating a type of market of useful forest products.

The team found enticing evidence that suggests that the biodiversity of some of the remaining forests in Acre may have been influenced to a large degree by these ancient ‘agroforestry’ practices. Dr. Watling did however note that it is certain that Acre’s forests were never cleared for as long, or as extensively, as they have been in recent times, in spite of the large density and number of geoglyph sites in the region,









Watling also strongly cautioned that the evidence that indigenous peoples have managed the Amazonian forests long before European Contact should not be used to justify the destructive and unsustainable land use practiced nowadays. It should rather serve to emphasize the importance of native knowledge for finding more ecologically sustainable land use alternatives and the ingenuity of past subsistence establishments that did not lead to wiping out forests.

The team dug up soil samples from a series of pits outside of, and within the geoglyphs, to conduct the study. From these samples, a type of microscopic plant fossil made of silica called ‘phytoliths’ was analyzed.

This enabled the team to reconstruct the following:

Carbon stable isotopes were used to determine how overgrown the vegetation was in the past.

Charcoal quantities were used to evaluate the amount of ancient forest burning.

Ancient vegetation.

Save

Save