How archaeologists found the lost medieval megacity of Angkor

The ornate, pinecone-shaped towers of Angkor Wat in Cambodia float above a vast temple complex of shrines, pools, houses, and a perfectly square moat. Today, only a small number of monks remain within the temple walls. The remaining structures have been reclaimed by trees whose roots wind around the stone like cellulose tentacles. Archaeologists have long wondered what life was like here when Angkor was the cosmopolitan heart of the Khmer Empire in the 12th and 13th centuries. Why did so many people abandon this place in the 15th century, never to return?

Unlike a majority of archaeological endeavors, the answers didn't come from digging up the ground. Instead, our first glimpse of Angkor as it once was came just a few years ago from a sophisticated laser scanning machine mounted on a helicopter.

For centuries, the Angkor region's wealth of artifacts drew looters, archaeologists, and looter-archaeologists. They focused their attention, both good and ill, on Angkor Wat and a few other nearby moated temple complexes. Based on those ruins, the first European explorers to encounter Angkor in the 19th century assumed Khmer urbanites lived in what were basically moated cities of a few thousand people. These European explorers thought Angkor Wat was something like a medieval walled city in Europe, which typically held fewer than 10,000 people. They explained all the moated complexes in the Angkor area by suggesting that maybe the royal family and their people were moving from one moated city to the next over time. But as archaeologists learned more in the intervening century, something about those population numbers seemed off. Beyond the moated cities were vast canal systems and reservoirs hinting at something bigger.