At 6 million square kilometres, the enormity of the Amazon Rainforest is difficult to comprehend.
If you started at the eastern edge and walked 3000 kilometres westward, you still wouldn’t emerge from the dense canopy. In this vast ocean of trees, huge swathes remain unexplored by modern scientists and archaeologists.
Today, the Amazon Rainforest is home to at least 100 uncontacted human tribes, an unimaginable reality in today’s hyperconnected world. Living in small groups, these indigenous people are generally nomadic, moving with the seasons through their territories and surviving by hunting and foraging the land.
But has this always been the case? Recent evidence suggests that a vast network of ancient cities once thrived in this modern-day wilderness.
Rumours of Lost Cities
The first clues about these lost cities come from the first Europeans to penetrate the rainforest in 1542.
The colonists reported teeming cities, roads, and fertile fields. “There was one town that stretched for 15 miles without any space from house to house”, wrote Gasper de Carajal, chronicler of explorer and conquistador Francisco de Orellana.
These accounts were convincing enough to raise funds for a second expedition three years later. However, this venture was seemingly cursed from the start: two ships were lost midway across the Atlantic, men were lost to illness and desertion, and the survivors resorted to cannibalism. The deadly misadventure claimed the lives of most of the crew, including Orellana himself.
The Amazonian cities were largely dismissed as fantasies concocted by Orellana to impress the Spanish crown, never seen nor written of again.
For some, however, the possibility endured; perhaps the most famous case was Percy Fawcett, a British archaeologist who dedicated his life to seeking the “Lost City of Z”, a supposedly hidden Amazonian city of immense wealth. Fawcett never realised his dream: he disappeared after setting off on a final expedition in 1924.
By the 21st century, it was well-established that the Amazon was always a green desert, sparsely populated by small nomadic tribes.
New Discoveries
Over the last 20 years, excavations in the Llanos de Mojos, an area of the southwest Amazon rainforest, have uncovered evidence of the “Casarabe Culture”, an ancient society named after a nearby Bolivian village.
Estimated to have emerged around AD 500, very little is known about these mysterious people. Until recently, experts assumed that the Casarabe people were nomadic hunter-gatherers, much like the present-day isolated Amazonian tribes. However, this archaeological dogma is now being challenged.
In a new study published in Nature, researchers used a helicopter equipped with LiDAR to search six areas of the Amazon that have been confirmed to have been occupied by the Casarabe people.
LiDAR (“light detection and ranging”) works by firing rapid pulses of laser light. Some pulses find through the tiny gaps in the dense canopy, travel to the forest floor, and get reflected back to the LiDAR sensor. LiDAR uses the time taken for the light to travel to the ground and back to calculate the distance travelled, which is converted to elevation. Taking millions of these measurements per second, LiDAR was used to construct a high-resolution 3D map of 200km2 of the southwest Amazon.
Secrets Beneath the Canopy
What LiDAR revealed was unprecedented: a constellation of 26 interconnected towns, two of which covered an area of more than 100 hectares – three times the size of the Vatican City.
The architectural complexity of these settlements is mind-blowing; there are artificial terraces, the remains of U-shaped “ceremonial” buildings, huge earthenware platforms, and conical pyramids over 20 metres tall. This network is interconnected by an impressive system of causeways, which radiate out from the two larger urban centres like spokes on a wheel, stretching for several miles. Researchers described this as a “low density” urban sprawl, somewhat analogous to a large city fringed by suburban towns.
Surrounding these settlements, LiDAR revealed sophisticated water management infrastructure, boasting large reservoirs and 965km of canals. These waterways were likely an irrigation system for large-scale agriculture across the region.
Indeed, analysing ancient pollen samples and soil chemistry in the area has revealed that the Cassarabe people cultivated a rich diversity of crops, including maise, squash, sweet potato and even cacao and Brazil nuts. These discoveries defy long-standing beliefs that ancient Amazonian societies were hunter-gatherers; instead, they were agriculturists whose activity has left scars on the landscape still visible 600 years later.
In the wake of these discoveries, a wealth of questions are raised. How were these societies organised? How many people lived there? Did the pyramids serve some religious purpose? Perhaps most intriguingly, what happened to the Casarabe people?
Radiocarbon dating has revealed that after some 900 years, human activity ceased in the area around 1400, before the arrival of European colonists. In the rapidly changing Amazonian landscape, researchers will need to work against time to survey these regions before evidence is wiped away by deforestation and intensive agriculture.
by Anna Flemming (she/her) is a graduate of medical sciences.
