With a population that approached 1 million and a surface area of more than 115 square miles, the Khmer city of Angkor in Cambodia was the largest preindustrial settlement on the planet. After coming into being during the ninth century A.D., it thrived for 6 centuries as a central hub for commerce and art — rising to eventually become the capital of the Khmer Empire — before it started its rapid and heretofore unaccountable decline. Until very recently, archaeologists had suspected warfare and changing religion were at the root of the settlement's collapse.
A new study has now shown that the key to Angkor's demise may have lied in the technology that made its rapid ascent possible: its highly sophisticated hydraulic system. A technology originally devised to help the city's residents manage and harvest water during the dry season — which involved diverting three major rivers through Angkor's agricultural fields, homes and temples — facilitated their demise when overpopulation and deforestation caused its canals to become filled with sediment. The elaborate waterworks required an extensive redesign of the city's landscape and natural resources — manual labor-intensive changes that soon became unmanageable. According to archaeologist Damien Evans, the lead author on the study, the system thus became "not manageable, no matter how many resources were thrown at it."
Evans and his colleagues employed a variety of old and new technologies — including a synthetic radar unit managed by NASA, an ultralight aircraft flown over the city to take photographs and motor scooters used to examine sites in the city — to reach their conclusion. The radar images provided a comprehensive picture of soil density, moisture and local structures which, when combined with the photographs taken from the aircraft, enabled the researchers to find and examine the city's characteristic temples and artificial ponds used for irrigation and water storage.
Having created a partial map 3 years ago, the researchers, known collectively as the Greater Angkor Project, released an updated one on Monday that contained an additional 386 square miles of urban area, 74 temples and more than 1,000 newly observed artificial ponds.
Evans and his team now plan on further exploring the city's ruins to understand what exactly happened during its collapse: "We're going now and excavating [the sites] on the ground, and trying to get a grip on when they happened -- whether they were a precursor of the decline, a symptom or the system gradually falling into ruin after they left."