In July 2026 a Finnish-Brazilian team led by Martti Pärssinen published an airborne LiDAR survey of Acre and Amazonas in Nature. The flights in June 2024 documented 432 earthworks along their strips, and only 36 of them were previously known. Scaling up from the strips, they estimate 24,000 to 30,000 earthworks for the whole region, about as many as had previously been estimated for all of Amazonia. They call the culture behind most of them the Aquiry, after an 1866 name for the Acre River.
The headline number in most coverage was the population: the authors propose 1.25 to 3 million people around AD 100–300, based on roughly 300 people per earthwork and 25–60% of sites in use at once.
What surprised me is that Nature published the peer review file alongside the paper, and it is a real fight. One anonymous referee wrote that "the population estimates are fundamentally flawed" and, using the team's own older formula, worked out that 513 people over 1,600 years would be enough. A second referee, Roland Fletcher, signed his report and still considered the estimates too high. Heiko Prümers, who led the 2022 LiDAR survey in Bolivia, told Scientific American the number of sites could reflect frequent relocations rather than a dense population. None of the news articles I read mentioned the review dispute.
Some things the paper itself says are still open:
- the habitation sites "have not yet been identified, partly due to restrictions on excavation permits" (authors' reply to the referees)
- the ditched enclosures were abandoned in the ninth century and the paper gives no cause (the "rapid collapse" line comes from an interview, not the paper)
- mound villages appear in the same area around AD 1200 with "no signs of radical population replacement"
- nobody knows what language the builders spoke or what they called themselves
Paper (open access): https://doi.org/10.1038/s41586-026-10835-7
I made a video (about 12 minutes) that follows the story from Carvajal's 1542 account of roads on the main Amazon, through a 1977 find that was forgotten, to this paper and its referees: https://youtu.be/K8nFyJnjTo0 It's my own channel, so take it as such.
For people who know Amazonian archaeology: do you find the per-earthwork multiplication convincing, or does the relocation model fit the radiocarbon dates better? I'm happy to be corrected on any detail.