Flying 4,400 kilometres of survey lines over 4,500 square kilometres of Acre state, a team led by Martti Pärssinen used airborne laser scanning, which reads the shape of the ground through the leaves, to find 396 earthworks nobody had recorded. Each is a geometric figure cut into the earth, a circle or a square with a deep ditch and a raised bank, some of them hundreds of metres across. Around 1,700 are now known across south western Amazonia, and because most of the region has still not been scanned, the researchers estimate more than 20,000 are out there under the canopy. Their study, Over 20,000 precolonial earthworks in the Southwest Amazonia, was published in Nature on 31 July. Acre alone, they say, appears to hold as many earthworks as the whole Amazon basin was once thought to have.

Laser scan images of circular and square earthworks under the Amazon canopy
Aquiry earthworks and roads seen through the canopy by laser scanning. Image: Pärssinen et al, Nature (2026), CC BY 4.0.

Read the full story: LiDAR reveals hidden Amazon earthworks from lost civilization of up to 3 million people, by Dario Radley, Archaeology News.

Who built them? In 2021 the same researchers gave the builders a name, Aquiry, from the Acre River, which means river of caimans in the language of the Arawakan peoples. They were at work from about 500 BCE to 850 CE. From the labour it took to dig and keep up so many earthworks, the team estimates a population somewhere between 1.25 and three million people at the peak, around 100 to 300 CE. Nobody lived inside the rings. They were ceremonial and gathering places; people lived nearby in long houses shared by several families and grew corn and squash. Oral traditions of Indigenous communities in the region hold that the earthworks linked neighbouring groups and carried spiritual meaning. Then, between about 850 and 950 CE, the building stopped, for reasons no one yet knows, at about the same time the Maya cities, Tiwanaku and the Wari were also thinning out. Over the centuries the forest came back over the rings, and it took a laser from above to see them again.

Our short take: the full story is by Dario Radley for Archaeology News (31 July 2026), from the paper by Martti Pärssinen and colleagues in Nature (2026).