The ruins of a gigantic Mayan city have been discovered under the blanket of the Guatemalan jungle. Using light detection and ranging (LiDAR) technology to see how the landscape would look without trees, the researchers found more than 60,000 previously unknown structures in the area, running the gamut from houses, walls and roadways, to huge pyramids and palaces. The researchers estimate the population of this ancient city could have been between 10 and 20 million people.