Lasers have revealed a complex network of pre-Hispanic structures and roadways hidden beneath the canopy of the Amazon. At 2,500 years old, it’s the earliest (and largest) example of an agricultural civilization ever recorded in South America’s dense rainforest.

Archaeologists have been studying the Upano Valley site, located along a stretch of the eastern Andes, for several decades. However, it wasn’t until they began viewing the Ecuadorian landscape using airborne lidar (light detection and ranging) — in which thousands of infrared laser pulses are reflected repeatedly off the landscape to reveal structures hidden beneath the vegetation — that they realized how elaborate the civilization actually was, according to a study published Thursday (Jan. 11) in the journal Science.