From the 9th to the 13th centuries, Angkor was the center of the Khmer Empire and the largest city in the world. Roads and canals connected the sprawling complex, which included hundreds of temples. But it didn't last.
Today, two million people each year visit the site in Cambodia, though much of it is in ruins. Archaeologists and historians have been uncertain about the reason for Angkor's decline, but they have speculated that war with the Thais may have contributed to the city's downfall or that the Khmer may have moved their capital to Phnom Penh to make it easier to trade with the Chinese. However, an international group of scientists is now arguing that climate change may, too, have played a role. Their study will be published this week in PNAS.
During its dominance, Angkor covered an area of nearly 400 square miles. To maintain such a large society, the city had a vast infrastructure that was dependent on the annual monsoons to flood the the region's lowlands and support agriculture. A new analysis of tree ring data from nearby Thailand and Vietnam, though, shows that the area experienced decades-long periods of drought during the 14th and 15th centuries, interspersed with intense monsoons.
The Khmer would have been unable to quickly adapt their large network of reservoirs and canals during the periods of drought, the researchers say, and agriculture would have suffered. Serious flooding during the monsoons damaged that same infrastructure that the farms depended on. Additional economic and political stresses would have combined with the climate and resulting agricultural problems, the scientists say, and contributed to the city's collapse.