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‘Lost’ Amazonian cities hint at how to build urban landscapes without harming nature

  • Archaeologists have discovered the remains of a Pre-Columbian urban settlement that spans more than 4,500 square kilometers (1,737 square miles) in Bolivia’s Llanos de Mojos region, in the Amazon rainforest.
  • This is the latest proof that large, complex urban societies existed in the Amazon before the arrival of the Spanish, challenging the idea that the rainforest was always a pristine, untouched wilderness.
  • Some experts say we could learn from these Indigenous urban planning strategies, which, with a sophisticated land and water management system, show us how cities and the rainforest once co-existed without degrading the environment.

It was over twenty years ago when locals in Bolivia’s northern plains told archaeologist Heiko Prümers, with the German Archaeological Institute in Bonn, about mysterious mounds of earth in the nearby Amazon that showed signs of a hidden El Dorado. Surrounded by trees and covered in vegetation, it was hard to see what the mounds were exactly, but they caught Prümers’ interest. In 1999, he began excavating the site with a team of researchers, completely unaware of the massive discovery they were about to make.

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What they uncovered were the remains of a vast and dense network of pre-Colombian settlements spanning more than 4,500 square kilometers (1,737 square miles) in Bolivia’s Llanos de Mojos region. The findings, published in Nature magazine in May, are the latest proof that large, complex urban societies existed in the Amazon before the arrival of the Spanish, challenging the idea that the rainforest was always a pristine, untouched wilderness.

Screenshots from a 3D animation of the Cotoca site. Source: H. Prümers / DAI.

Some experts say the urban area, which was home to thousands of Indigenous people from the Casarabe culture for nearly 900 years, is an example of how cities could exist in the rainforest without degrading the environment. Settlements did not contribute to forest loss and included a sophisticated agriculture and water management system, with hundreds of kilometers of canals and causeways to distribute water to crops and reservoirs.

Though, Prümers himself is skeptical that there is something more “ecological” about the Casarabe way of life compared to other cultures as the root of the settlements’ abandonment is still unknown. However, he says it’s clear they were dependent on their environment and their ability to use the resources around them to adapt to changing weather patterns.

For almost a millennia, the population built and inhabited a complex urban environment consisting of terraces, fortification walls, pyramids and causeways in the Amazonian savannah, during intense periods of heavy rains and droughts.

“It’s a very interesting because [the settlements are] very connected with ecological factors, in regions that are so dependent on small differences in rain that can have devastating consequences,” Prümers told Mongabay from his home in Germany, adding, “there’s still a lot of [archaeological] work to be done in the future.”

Undeniably urban, without harming nature

Urban ruins are always hard to find among the thick vegetation of the rainforest. But using the Lidar technology – firing a laser from a helicopter to scan the land below – the researchers were able to digitally strip away this vegetation and produce a map of the area of about 200 square kilometers (77 square miles). Using traditional mapping mechanisms, this would have taken up to 400 years, says Prumer.

The Riegl VUX-1 scanner with a Trimble APX-15 UAV GNSS, attached to the Eurocopter AS350 helicopter. Source: H. Prümers / DAI.

This map revealed a series of reservoirs and settlements of differing sizes, which resemble small towns or suburban areas, scattered across the region. These were connected by a system of raised causeways and canals. Two larger settlement sites were found at the center of this sprawl, which could be considered the urban center.

These two central sites, known as Landivar and Cotoca, were massive, measuring 99,795 and 276,030 square meters (414,744 and 2.97 million square feet) respectively. They housed artificial terraces, large raised platforms and conical pyramids over 21 meters (70 feet) tall. Successive rings of moat and fortification walls encircled the sites.

Large and medium-scale pre-Columbian settlements have been found in other areas of the Amazon, including the Upper Xingu region in Brazil and throughout the southern Amazon rim.

But what makes the Llanos de Mojos unique is the sheer size of the area and the two large central settlement sites. This allows it to resemble a classic urban design with a clear monumental center surrounded by periphery neighborhoods, in contrast to the other archaeological sites that consist of networks of settlements that scatter the area with no such center.   

Screenshots from a 3D animation of the Cotoca site. Source: H. Prümers / DAI.

“There really isn’t any doubt about calling it urban,” says Micheal Heckenberger, anthropologist at the University of Florida, who was not involved in the project but has been studying urbanism in the Pre-Columbian Amazon. “And so, this ups the game in the Amazon.”

José Iriarte, an archaeologist at the University of Exeter and co-author of the study, says a lot more research is necessary to fully understand their topological findings, the Casarabe people and their lifestyle. This includes the possible population of Llanos de Mojos, which he can only say was “a lot.”

But one thing is certain, he says, their water management system was central to their urban design and fundamental to their survival.

“They were not degrading the environment, though they had made a lot of investment,” says Iriarte, referring to the time and effort needed to build the extended system of canals, causeways and reservoirs, which required extensive environmental intervention.

The researchers identified 957 km (594 miles) of canals and causeways crossing through the savannah, though this number is likely much higher, Iriarte told Mongabay from his home in Spain.

Co-author Carla Jaimes Betancourt descending from the central pyramid of the Cotoca site. Source: H. Prümers / DAI.

Some of these connected the settlements, which could be up to 1,800–3,970 meters (5,905-13,024 feet) apart in the more densely populated areas. This likely facilitated communication and transportation between the clusters of homes, as the elevated causeways made it easier to walk through the savannah during the rainy season, and the canals made it possible to travel by boat during the dry season, says Iriarte.

The other canals crisscrossed through the open savannah, likely to regulate water distribution, especially for their small crops of yucca, maize and other staple foods. This allowed the population to drain the fields during the flooding season and distribute water during the dry season. The sites also had fish ponds and reservoirs to collect water for the dry season, which could last up to three months.

It’s also important to note, says Iriarte, that even though the Casarabe were dependent on agriculture, there is no record of large-scale forest loss in the region during this time period, according to his own separate studies analyzing the pollen records in the area.

Even though there was less forest in the savannah in general, there is no record of additional forest loss during this time, he says.

There are perhaps two reasons for this, he explains. It was harder to cut down large swaths of trees, as they didn’t have the tools. In areas where they did remove trees, they converted the area into orchards and planted others, or used it for crops and rotated them accordingly for soil preparation and maintenance.

A photo mosaic from drone footage at the Salvatierra site. Source: H. Prümers / DAI.

“We should see it as a mosaic of plots in different stages of sucession, from the plot that has just been cut to plant the maize and beans and so forth, to the one that has been abandoned and is becoming little by little and orchard, and so forth,” says Iriarte. “So that’s why we call it like, polyculture agroforestry, because they are planting crops, but they are not entirely taking down the forest.”

This was a common practice in Amazonia from the start of the Holocene period, which he explores at length in a separate study, challenging a myth that Amazonian soils were so poor that they couldn’t sustain agriculture and large populations.

“When you see the bioecological record integrated with the archaeology, you see that they were creating new types of soils, like the Amazonian dark earth, or that they were creating these hydraulic engineering in the Llanos de Mojos,” says Iriarte, “But, you know, they were not degrading the environment doing this.”

Prümers is more hesitant about making conclusions on the Casarabe’s water or land management systems, saying more excavation and research still needs to be done to understand them properly.

“As long as we don’t know why they disappeared, I wouldn’t venture to say they were more ecological than other cultures,” he says, adding, “There’s so much data still missing, that it’s difficult to say why these people of the Casarabe culture were successful in their way of life for those 900 years.”

Dating at Llanos de Mojos suggests that the Casarabe people stopped inhabiting the city in 1400 C.E., about 100 years before the arrival of the European Colonizers, but it’s unclear why. Prümers suggests war, a pandemic or severe drought, a common occurrence in the Amazon during this time, are among a number of possibilities.

Other researchers say these findings are important to understand Indigenous technologies and strategies that could be reproduced today to create cities that operate in harmony with biodiversity.

Incachaca archaeological site in Bolivia. Image courtesy of Greg Keelen on Unspash.

An alternative model for urban planning?

Heckenberger has worked for decades in the Upper Xingu region in the north of Brazil, where a large network of pre-Columbian settlements spans the area. He estimates that some 50,000 people lived here over 500 years ago, until the Spanish arrived. It’s worth paying attention to how such a large population was able to survive in a region that’s seen as hostile to humans, he says.

This site differs from the Bolivian case in several ways. Mainly, it’s located in a fully forested area in the Amazon, not the savannah, and it doesn’t have a monumental center location, like Llanos de Mojos.

But, like the Bolivia case, Heckenberger says the Upper Xingu shows an impressive level of environmental engineering. He refers to the area as a Garden City, a term made popular in 1902 by the British Urban planner Ebenezer Howard, who offers an alternative model of decentralized urbanism that favors open space and better land management.

In the Upper Xingu, settlements, or communities, surrounded by moats and ditches, are spread out through a vast forested area, but all interconnected via a series of canals, roads and bridges. The area around them served as essential tree cover, or was used for agriculture and fish farming. This food system used sophisticated canal systems, reservoirs, weirs, and crop rotation methods.

Mapping and monitoring of territory in the Xingu Basin of the Amazon. Image courtesy of Julian Moura-Busquets/People’s Planet Project.

“There’s a lot of simulations out there about the collapse of the Amazon. Well, none of them actually have yet taken Indigenous people and Indigenous pre-Columbian technologies seriously,” says Heckenberger. He adds that we could use this information to create sustainable urban models that work.

Recent studies suggest that 50% of the world’s population will be living in the tropics by 2050, due to rapid economic and population growth in the region. The same authors of the report, which include researchers from 12 tropical research institutions, say this could be a disaster if urban expanses aren’t controlled and more sustainable.

“The typical cement, no trees, air-conditioned cities in Amazonia are not going to work,” says Iriarte, calling them unsustainable heat traps with no tree cover.

“Obviously we’re not going to reproduce the past,” he says. “But hopefully we can take some lessons from this.”


Banner image: Incachaca archaeological site in Bolivia. Image courtesy of Greg Keelen on Unspash.

Related listening from Mongabay’s podcast: We speak with Scott Wallace, a journalism professor at the University of Connecticut, National Geographic writer, and author of a New York Times best-selling book on the importance of protecting uncontacted indigenous groups in the Amazon. Listen here:

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