Between 600 and 1,500 years ago, Indigenous people of the seasonally flooded savannas in the Bolivian Amazon created an advanced farming system that allowed them to grow corn throughout the year, according to a study published in Nature. These findings challenge what researchers know about early farming in South America.

A team of researchers led by Umberto Lombardo from the Autonomous University of Barcelona found evidence that the Casarabe culture, whose people lived in the Llanos de Moxos region of Bolivia  built an impressive network of drainage canals and artificial ponds between 500 CE and 1400 CE. This water management system worked with the natural seasonal changes of the Amazon Basin.

During the rainy season, the Llanos de Moxos region would flood. To handle this, the Casarabe built drainage canals to remove excess water from their fields. These canals varied in size, according to the researchers. When the dry season arrived, the artificial ponds retained water, allowing farmers to irrigate their corn crops by hand. This meant they could grow corn year-round instead of just during certain seasons.

“The pond itself is cultivated,” Lombardo told Mongabay. “So, the idea is that they had these ponds with the water in the middle, and the maize was cultivated on the edges of the pond.”

The study suggests that the Casarabe culture represents an example of a “Neolithic Revolution” in the Amazon, with an economy based on grain production that supported relatively large populations and complex social organization, a history long hidden beneath the forest canopy.

To piece this story together, researchers used advanced technology to map the landscape and examined tiny plant remains under microscopes. By analyzing 178 plant microfossils (phytoliths) and pollen found in an old farm pond, they confirmed that corn was the main crop that sustained this pre-Columbian society’s diet. “The data shows the absence of other types of crops,” Lombardo said.

The Casarabe weren’t just skilled farmers. They also built enormous earthen mounds as part of their settlements. “It’s hard to imagine how big they are,” Lombardo said. “An average monumental mound covered the area of 20 football fields — like 10 hectares [25 acres], 15 hectares [37 acres] — and can be up to 20 meters [65 feet] high. These are huge mounds made of earth. Of course, they built this across 1,000 years.”

Many of these ancient structures remained hidden until recently because they’re covered by forest. The research team used special technology called lidar, mounted on drones, to see through the forest canopy.

“With lidar, you see everything super clearly, all the canals,” Lombardo said. “You just remove the forest. It’s magic.”

These settlements were connected by roads and canals, forming what researchers call low-density urbanism, cities spread across the landscape rather than concentrated in one area.

“We are starting to find evidence of really complex societies in the Amazon,” Lombardo said. “When you start looking at the maps, you actually realize that it is like a huge city of tens of square kilometers, with very low population density compared to a European city.”

The landscape today gives few clues to its engineered past. Now, the landscape looks like stripes of forest across the savanna. Yet the forest grows along old river channels where sediment was deposited. These areas remained elevated and were less prone to flooding.

Alder Keleman Saxena, an expert not involved in the study, explained why these societies remained unknown for so long. Yellow fever, malaria and other illnesses to which Indigenous Americans had no immunity “raced across the continents, and killed some 90% of the population before colonizers from the Old World had begun to establish a foothold,” Keleman Saxena, assistant professor in the Department of Anthropology and program in sustainable communities at Northern Arizona University, told Mongabay in an email.

This massive population loss has distorted our historical understanding of Amazonian societies, according to Keleman Saxena. “Among the consequences of these introduced pandemics is the fact that there are very few existing records of what Indigenous societies of the Americas looked like before European contact — and this is particularly true for regions that were hard for invading forces to reach, like the lowland Bolivian Amazon.”

The research shows that rather than clearing forests through slash-and-burn agriculture, the Casarabe people preserved the forests and focused their agricultural activities on engineering the savanna areas. This forest preservation was likely intentional, as the forests provided valuable resources like firewood, building materials and medicinal plants.

The study provides evidence that there was no charcoal or signs of fire in the forest soil samples, indicating the absence of slash-and-burn practices. Additionally, the phytolith analyses showed no cultivar phytoliths in the forest samples, further supporting that the Casarabe people were not cultivating crops in the forest areas.

“Now, the consensus is that most of the Amazon, the type of pre-Columbian land use was mostly agroforestry,” Lombardo said. “They didn’t actually cut down the forest, but they just helped some type of trees to grow because they’re useful and maybe eliminating those that are useless for them. They basically changed the composition of the forest a bit, but they never cut down the forest.”

“These projects allow us to see that these now-forested landscapes were once densely populated urban areas, and that relied on sophisticated agroecological techniques to support large and complex societies,” Keleman Saxena said. “These findings have the potential to offer insights on the possibilities for small-footprint living in the context of the current climate crisis; and they also provide important vindication for contemporary Indigenous people of the Americas, who continue to occupy, cultivate and advocate for political sovereignty over these territories.”

Banner image of artwork of the ponds described in the paper (Lombardo et al 2025) created by Julian Puig Guevara.

Citation: Lombardo, U., Hilbert, L., Bentley, M., Bronk Ramsey, C., Dudgeon, K., Gaitan-Roca, A., … & Mayle, F. (2025). Maize monoculture supported pre-Columbian urbanism in southwestern Amazonia. Nature, 1-5. doi:10.1038/s41586-024-08473-y    

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