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Archaeology: Aerial imaging uncovers scale of Amazonian civilization
Aerial imaging has detected 432 patterns called earthworks, on the ground in southwestern Amazonia, a paper in Nature reports. The findings were made in an area previously inhabited by the ancient Aquiry civilization of southwestern Amazonia, and the region may contain 24,000–30,000 earthworks. The findings may help to redefine the true scale of Amazonian earthworks and the communities that built them.
Large geometric ditched enclosures, known as Amazonian geoglyphs, left by the ancient Aquiry civilization are thought to have functioned as ceremonial, political and public gathering centres. The mostly solitary structures are composed of ditches and embankments and range from 0.35 to 14 hectares in size; the largest known geoglyph covers nearly 50 hectares. Previous attempts to estimate the number of earthworks across Amazonia are limited because they are based on sites discovered in deforested areas (where archaeological features can be detected with relative ease). A form of aerial survey known as LiDAR (light detection and ranging) can reveal structures concealed beneath dense rainforest canopy.
Martti Pärssinen and colleagues carried out LiDAR surveys over an area of 4,497 km² in southwestern Amazonia, including around the cities of Rio Branco, Lábrea, Boca do Acre and Carauari in Brazil. Their dataset yielded 432 earthworks, of which 396 were previously undocumented. By extrapolating these results, and in combination with existing satellite studies, the authors suggest the Aquiry region, composing around 183,000 km², may contain 24,000–30,000 earthworks. In addition, they estimate that the Aquiry civilization supported approximately 1.25–3 million people at its peak between AD 100 and 300, which suggests that it left a greater impact on Amazonian soils, forest structure and biodiversity than previously thought.
The Aquiry civilization occupied an area equivalent to less than 3% of Greater Amazonia, yet the region may contain more earthworks than previously predicted for the whole Amazon basin. The authors conclude that should similar concentrations of earthworks occur elsewhere, estimates of precolonial populations and their local impact should be reassessed.
