Lost Cities of the Amazon Discovered From the Air

The Amazon is one of the planet’s last great wildernesses, but legends have circulated for centuries that lost cities existed deep within the forests. A search for El Dorado, a supposed city of gold, lured many Spanish explorers far off the map, and some of them never returned. As recently as the 20th century, British explorer Percy Fawcett searched for what he believed was the Lost City of Z. He vanished into the jungle and added his own unfinished chapter to a tale that began 600 years ago.

Now the plot has taken a new twist, as scientists have discovered that ancient cities really did exist in the Amazon. And while urban ruins remain extremely difficult to find in thick, remote forests, a key technology has helped change the game. Perched in a helicopter some 650 feet up, scientists used light-based remote sensing technology (lidar) to digitally deforest the canopy and identify the ancient ruins of a vast urban settlement around Llanos de Mojos in the Bolivian Amazon that was abandoned some 600 years ago. The new images reveal, in detail, a stronghold of the socially complex Casarabe Culture (500-1400 C.E.) with urban centers boasting monumental platform and pyramid architecture. Raised causeways connected a constellation of suburban-like settlements, which stretched for miles across a landscape that was shaped by a massive water control and distribution system with reservoirs and canals. The site, described this week in Nature, is the most striking discovery to suggest that the Amazon’s rainforest “wilderness” was actually heavily populated, and in places quite urbanized, for many centuries before recorded history of the region began.

Co-author Heiko Prümers, of the German Archaeological Institute, references an old Spanish proverb asserting no one is so blind as the one who doesn’t want to see. “It’s a myth that was created by Europeans who really spoke of a jungle, and vast regions untouched by humans,” he says. “So a lot of people didn’t want to see that there were archaeological sites here that merit exploration.”

“I’m sure that in the next 10 or 20 years we’ll see a lot of these cities, and some even bigger than the ones we are presenting in our paper,” he adds.

Michael Heckenberger, an anthropologist at the University of Florida, wasn’t involved in the research but has been studying urbanism in the pre-Columbian Amazon for nearly two decades. He notes that elements of the settlement at Llanos de Mojos like moats and causeways, and a modified landscape of parklands, working forests and fish farms, have been seen elsewhere in the ancient Amazon. But the new research unveils something quite new. Previous examples of urbanism in the Amazon include the Upper Xingu region of the Brazilian Amazon, where Heckenberger works with the Kuikuro Nation. Such settlements might be described as groups of villages networked together. They aren’t technically urban, some experts have argued, because they lack clearly defined larger centers, with monumental architecture like platform mounds and U-shaped temples. But those urban centers can be found at Llanos de Mojos. “This is in my mind the clearest case of a fully urbanized Amazonian landscape,” Heckenberger notes. “It’s a marvelous piece of work. It shows really remarkable range of things that humans did in the past to work with their landscapes and work with larger and larger populations.”

Previous hands-on archaeological work and other remote-sensing efforts had revealed hundreds of isolated sites across more than 1,700 square miles of the Llano de Mojos region, including settlements inhabited year-round by the Casarabe, who hunted, fished and farmed staple crops like maize. Some 600 miles of causeways and canals had also been identified. But the logistical challenges of mapping them in a remote tropical forest hampered efforts to connect the dots and see if, or how, they were related to one another.

The remote, forested area is difficult to explore and the remains difficult to spot, even from the air. “There’s no way to know what’s down there until you get there, and when you get there you have problems trying to find and orientate the sites,” says Prümers.

So the team conducted airborne lidar mapping of six different areas, ranging in size from about 4 square miles to 32 square miles, for a bird’s-eye view of what was the heartland of Bolivia’s Casarabe culture between about 500 and 1400 C.E. From an aircraft, a lidar system fires down a grid of infrared beams, hundreds of thousands per second, and when each beam strikes something on the Earth’s surface it bounces back with a measure of distance. This produces an enormous cloud of data points, which can be fed into computer software that creates high-resolution images in which scientists can digitally deforest the Amazon. By scrubbing away trees, the maps reveal the Earth’s surface and the archaeological features on it. In this case, the images clearly showed 26 unique sites, including 11 that were previously unknown.

Among the 26 sites were two large urban centers, Landívar and Cotoca. They were already known to exist, but the new maps detailed their archaeological complexity and vast size (1.2 and 0.5 square miles, respectively). Each large center is surrounded by successive rings of moat and rampart fortifications. The sites boast artificial terraces, huge earthen-platform buildings and conical pyramids over 70 feet tall. All these impressive civic and ceremonial buildings are also oriented to the north-northwest, which scientists believe reflects a cosmological world view observed elsewhere at ancient sites in the Amazon.

The aerial view with trees stripped away revealed two centers, each anchored by a large network of regional settlements connected by numerous causeways. Those passageways radiate out from the centers like spokes on a wheel, and they stretch for several miles. These connect sub-urban settlements, ranging from small settlements closer to the centers to more distant and even smaller sites that may have been used as temporary campsites. Similarly, canals also stretch from the main centers and connect to rivers and Laguna San José, which apparently delivered water to Cotoca.

“Basically they remolded the landscape in terms of their cosmology, which is mind-blowing,” says Chris Fisher, a Colorado State University archaeologist not involved in the study who specializes in Mesoamerica. “The only problem is that this architecture was made from mud brick. So while at the time it was as fantastic-looking as anything in the Maya region, the Maya monuments have endured because they had limestone, while these just weren’t as durable.”

The Casarabe certainly aren’t as well known as the Maya. So who were they? A decade of archaeological work on in the region has shown that their culture was distinct, and the region they inhabited was likely an annually flooded savannah with riverside forests—rather than the vast unbroken stands of timber one finds in the area today.

Andean cultures, where monumental platforms, mounds and temples are prominent, aren’t geographically far away. But an influx of Andean people or their influence isn’t responsible for the creation of these urban areas, says Prümers: “The Andes are very well studied, and you won’t find any site of this type in the Andes, so we can say it’s not something that came from the Andes. It’s uniquely Amazonian.”

What happened to the Casarabe and their settlements remains a mystery, but dating at the sites suggests that their occupation ended around 1400 C.E.—prior to European arrival in the Amazon. Widespread drought may have been the culprit, Prümers theorizes. At various sites his team has found huge reservoirs for water storage, which isn’t something one would immediately expect in an Amazon region known for plentiful rainfall.

“Of course, we don’t know if these were for a drinking water supply, or to farm fish or turtles, but it’s very interesting that we do have them,” he says. “We know that there were severe droughts in the Amazon regions several times in history. That might have happened to this culture as well. It only needs one or two years of loss of crops of harvest, and people have to move.”

Though it faced an unknown end, the culture that thrived here adds to the growing evidence that the Amazon isn’t actually one of the world’s great untouched wilderness areas—and wasn’t even an unbroken forest until relatively modern times.

Paleoclimate studies have suggested that much of the Amazon forest is a lot younger than suspected, and that large swaths of the Amazon, perhaps a fifth, were actually open savannah environments before Europeans arrived in the Americas. Such an environment would have facilitated the type of landscape engineering that it’s increasingly evident was practiced by Amazonians, many of whom likely lived in urban or suburban settlements with a high level of sociopolitical organization.

Heckenberger has worked for decades in Brazil’s Xingu region, where dozens of communities he calls “garden cities” feature homes, plazas and palisade walls. Though the sites don’t have the much larger monumental centers found in Bolivia, they were connected by a system of roads, bridges and canals, all situated in a large engineered landscape of fields, fish farms and other features. Intriguingly, this low-density, urban culture—which was more like a cluster of suburban communities without an urban center—thrived in the same region where Fawcett vanished in search of his Lost City of Z.

Difficult as they can be to locate in the forest, earthworks clearly built by humans, designs known as geoglyphs, have been found in several other Amazon locales. In 2018, scientists using satellite images reported that large areas of Amazon forest in Brazil’s Mato Grosso state, once thought to have been sparsely inhabited at best, were dotted with villages and oddly shaped earthwork geoglyphs. Even here, away from large rivers, many hundreds of villages could have housed up to a million people between 1250 and 1500 C.E. in an area that represents only about 7 percent of the Amazon basin. However, if larger urban centers anchored these populated sites, they haven’t yet been identified.

Such discoveries of settlements were the result of very hard work. Despite the large and sophisticated populations that once thrived here, lasting evidence of urbanism has proved difficult to find in the remote and thickly forested Amazon. But lidar technology seems set to rapidly boost the pace of future discoveries. “Lidar has been transformative for archaeology and this work is a great example of that,” says Fisher.

“These researchers were able to see patterning that’s just not visible from the ground, and that pattern clearly showed two very large settlements, embedded within a settlement system, with a level of social complexity that really hasn’t been demonstrated very well in the Amazon,” he says. “It’s absolutely amazing.”

While it appears that the Amazon once teemed with human activity, many ancient sites have remained almost undisturbed for some 500 years, something Prümers cites as a big advantage. “The region has very low population density, and that means that we are finding the relics of pre-Spanish cultures over there almost untouched,” he says.

But the Amazon is changing rapidly. Forests are being eliminated to promote farming, ranching, energy production and the roads and dams that support such efforts. Many of those undisturbed areas, with their hidden records of past cultures, won’t remain so for long. Fisher advocates for large-scale lidar scanning of the Amazon, and far beyond, through an Earth Archive project aimed at capturing what remains of the past before it’s lost to the future.

“We’re running out of time, because we’re losing the Amazon,” he says. “And we’re going to lose things that we never knew were there. To me, that’s a real tragedy.”

Brian Handwerk | READ MORE

Brian Handwerk is a science correspondent based in Amherst, New Hampshire.