This SciShow video is supported by LMNT.

You can head to DrinkLMNT.com/scishow for a free sample pack of  electrolyte drinks with any order. [♪ INTRO] To learn about the people and  societies that existed long before us, we often have to literally dig up the past. Excavating historical sites  is one of the major ways archaeologists piece together human history.

But it’s not easy to find every  interesting site, let alone excavate it. The traces of many major civilizations  are buried in hard-to-reach places. That’s why scientists are now using  lasers to scan the ground for structures that might have been built by ancient people, offering clues about where and how they lived.

One place archaeologists are  especially interested in is the Amazon. This region has been home to indigenous  groups for thousands of years, since long before the arrival  of Spanish colonizers. In the past, archaeologists  assumed that these people lived in small, isolated groups  rather than larger societies.

In fact, many considered the region  unsuitable for permanent settlement. So researchers figured that the Amazon  never had sophisticated societies that might have transformed the environment  through things like irrigation or agriculture. That notion helped create an image of  the Amazon as this pristine environment, unaffected by humans until modern times.

But a growing amount of evidence suggests…  that may be anything but the truth. For instance, satellite images and  archaeological expeditions in recent years have revealed some human  settlements in the southern Amazon. But it was not clear how extensive they were.

Researchers also couldn’t tell if  they were related to each other or just self-contained sites. But there was reason to believe  they could be connected. In historical accounts from the 1600s,  Jesuit missionaries in this region described large villages with what they called  powerful chiefs and influential shamans.

So, archaeologists began to  wonder if this could be true. It’s well established that  between 500 and 1400 CE, a people known as the  Casarabe lived in this region. They inhabited a tropical  savanna called Llanos de Moxos.

So, archaeologists became intrigued by  the possibility that the Casarabe had developed a sophisticated agricultural  civilization in what’s now a tropical rainforest. If they had, it would suggest  that human civilization may have left a footprint  on the Amazon rainforest: this place that was considered  “untouched” before modern times. But actually investigating  this question was a challenge.

The Amazon is vast and full of rough terrain that makes it hard to explore  through ground expeditions. And an aerial view won’t offer many clues  because the tree cover is too dense. So, in a 2022 study, researchers  turned to a relatively new tool: lidar.

Lidar works by bouncing pulses of laser  light off the ground from the air. Since light travels at a fixed speed, lidar  detectors can tell exactly how far away the ground is based on how long it  takes the laser pulse to bounce back. So, by scanning an area with lidar, researchers can actually  construct 3D maps of the surface.

Lidar can’t pass through trees, but  enough pulses will make it through gaps in foliage that this technology can  be used to map out forest floors. So the researchers in this study  decided to use lidar to look for possible human-made structures  beneath the trees in Llanos de Moxos. They launched lidar pulses from a  helicopter down into the Amazon.

And what they found was incredible. In all, they identified 26 sites with structures that appeared to have been  built by the Casarabe people. These structures were organized into  what the researchers described as an urban-like system: essentially, a group  of cities and smaller settlements.

These weren’t cities like New York or Chicago, where many people live together  in a tightly packed area. They were more like large population centers  surrounded by collections of settlements. These centers were protected by curved  moats and defensive walls, and they were connected to the smaller surrounding  settlements by raised causeways.

Kind of like how today’s cities  are linked to smaller towns. This design suggests that  some people would have lived out around their farms or hunting grounds, but they would have been well  connected to the population centers. Another thing that stood out  about these urban systems was how well they managed water.

At the time the Casarabe lived, the  region wasn’t covered in trees yet. Instead, it flooded seasonally, and went  through cycles of droughts and floods. So it took some engineering to have a  steady supply of water that could support a major civilization.

But the Casarabe were up to the task. In the lidar images, researchers  found large reservoirs. And around one of the population centers, they found canals connecting  it with rivers and a lake.

All this evidence indicated that ancient people  hadn’t just lived passively in the rainforest. They had redirected water and reshaped the land, transforming this tropical region  into an agricultural landscape. This finding settles the debate about  whether or not people developed settlements in the southern Amazon before  the arrival of Europeans.

In fact, not only did the Casarabe settle  there, they developed a civilization far more sophisticated than anyone  expected to find in this region. Finding this type of urbanism in the  Amazon, of all places, highlights the fact that rainforests are not always  pristine, untouched environments. In fact, the Amazon may not be the only  rainforest to have hosted an ancient civilization.

It’s possible that other dense rainforests,  like the Congo Basin in central Africa, could have seen urban development in the past too. And as lidar gains strength  as an archaeological tool, scientists are in a better place to  get to the bottom of these questions. Now if they were going to try to  reach these civilizations on foot, they might benefit from LMNT.

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It just has sodium, potassium, and magnesium. That means it’s vegan friendly and gluten free. And if you don’t like it, they’ll give you your  money back with a no-questions-asked refund.

Right now, LMNT is offering SciShow  viewers a free sample pack with any order. That’s eight single serving  packets free with any LMNT order. It’s a great way to try all eight  flavors or share with a friend!

You can get yours at DrinkLMNT.com/SciShow. That's DrinkLMNT.com/SciShow. Thank you to LMNT for supporting this  video and thank you for watching! [♪ OUTRO]