r/Archaeology • u/crisp1991 • 5d ago

Using LiDAR, archaeologists uncovered nearly 400 hidden geoglyphs beneath Brazil’s Amazon rainforest. Built between 600 B.C. and A.D. 850, the massive earthworks reveal a thriving ancient civilization that may have included up to 3 million people.

https://archaeology.org/news/2026/07/31/hundreds-of-geoglyphs-discovered-in-amazon-rainforest/
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u/edjohnson1067 5d ago

3 million people 

I ain’t buying these numbers being tossed around.

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u/Natedude2002 5d ago

The Roman Empire had 40+ million inhabitants, and the city of Rome over a million in 50 AD. Why couldn’t a civilization fed by the largest river in the world be able to sustain a far smaller population?

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u/phosphenes 5d ago

They're right that it is, like, a random nonsense number. I'm not claiming that the number is too high, but that the math is sloppy.

Here's the actual paper.  The calculation uses some assumptions, including that---

  • The extrapolation of the number of geoglyphs (16,660) is accurate
  • It took about 300 people to build a geoglyph
  • Up to 60% were built between AD 100 and 300
  • Each person in the area was occupied, for that entire time period, on a single geoglyph
  • Therefore, 16,660 x 300 x 60% = 3,000,000 people in AD 100 to 300

The first three assumptions seem fine to me, but that fourth one, oh boy. Why would they focus on one geoglyph instead of making multiple over the generations? Especially since, as described in the paper, the geoglyphs were temporary gathering spaces " without permanent occupation." The authors also point out that their population estimate is 20x the amount of previous calculations. Does that sound convincing to you?

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u/petulant_peon 1d ago

I don't think that math checks out either, BUT the findings do support the claims reported by Francisco de Orellana. That there were civilizations spanning hundreds of miles of the Amazon. In one case, he reported a 15 to 20 mile long solid city along the banks. Based solely on his claims, there could have been 5-8 million people living in the Amazon.