In the modern day, archaeologists make many of their discoveries not by traipsing through the jungle Indiana Jones-style, but with high-tech scans. Now the ruins of a gigantic Mayan city have been discovered under the blanket of the Guatemalan jungle, by bouncing lasers through the trees to reveal thousands of previously-unknown structures.

It can be hard to spot and study ruins in the thick jungles. The undergrowth can impede progress on foot, while the heavy canopies overhead can hide everything from an aerial view. Frustrating as that may be for archaeologists, getting rid of the trees is obviously not the answer – at least, not physically. This project used light detection and ranging (LiDAR) technology to see how the landscape would look without trees, in a process the team calls "digital deforestation."

LiDAR works by beaming a laser from a device, bouncing it off a surface and measuring how long it takes the light to return to a sensor in the device. It's widely used as a method for precisely measuring distance, conducting chemical analyses, and it forms the core of navigation and obstacle avoidance systems in autonomous vehicles.

In this case, the LiDAR device was mounted on a plane flying over the jungle, constantly beaming laser pulses towards the ground. Since the laser beams were able to slip through tiny gaps between the leaves and branches, most of the light hit the ground before bouncing back, and with a little algorithmic help afterwards, the data can be translated into a detailed topographical map of the terrain, sans trees.

In 2016, aerial surveys imaged 2,100 sq km (810 sq mi) of Guatemalan jungle, including major Mayan sites such as Tikal and El Zotz. The LiDAR scans revealed more than 60,000 previously unknown structures in the area, running the gamut from houses, walls and roadways, to huge pyramids and palaces.

"In that kind of environment where you can't see [a few feet in front of yourself], it's very hard to piece that all together," says Thomas Garrison, an archaeologist from Ithaca College who helped conduct the surveys. "You have this idea that there's some little stuff on the hills, but the LiDAR lets you see it in its totality."

The new discoveries shed light on the mysterious Mayan civilization, which rose to prominence in the area about 4,000 years ago and reached its peak around the 9th century AD. Agricultural features reveal how the society was able to sustain itself for so long, and defensive structures like walls and towers suggest that warfare may have been more common than was believed.

With the expanded city comes an expanded population. The researchers have now bumped up the estimated population from a few million to between 10 and 20 million.

A second LiDAR survey is currently in the works for another area, and the archaeologists say the next steps include physically visiting the newly-discovered ruins.

The project was conducted as a collaboration between archaeologists from the US, Europe and Guatemala, and PACUNAM, a cultural heritage preservation organization. The discoveries will be the subject of a National Geographic documentary airing this week in the US.

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