We've mapped a huge settlement beyond the main temples at Angkor using radar imaging and other satellite data," said Damian Evans, a deputy director of the University of Sydney-based Greater Angkor Project. "This is the first time a complete, detailed and comprehensive map of Angkor has been presented," he said.

Carpeted with vegetation and obscured by low-lying cloud, the ruins spill over 1,000 square kilometres outside the World Heritage site, located in present-day Cambodia, and are linked by a complex water management system.

Reconstruction of battle scenes depicted on temple bas-reliefs.
(Credit: Tom Chandler, Monash Asia Institute)

Mr Evans and colleagues from Australia, Cambodia, and France have worked for years to integrate information from hand-drawn maps, ground surveys, airborne photography, and ground-sensing radar provided by NASA.

"The radar can sense differences in plant growth and moisture content that result from topographical variations of less than a meter," Mr Evans said. "We have identified over a thousand new manmade ponds and at least 74 long-lost temples, by correlating the radar data with on-the-ground sampling."

One single hydraulic system links the entire network, which appeared to provide Angkor's citizens with a stable water supply despite the unpredictable monsoon season.

The system, thought to be purely decorative and ceremonial by many scholars for the past 30 years, may actually have been used for irrigation and the intensification of rice agriculture.

Mr Evans said there "are also signs that the large-scale city engineered its own downfall by disrupting its local environment by expanding continuously into the surrounding forests and exposing the water management system to increased sedimentation and erratic water flows."

This caused a radical re-engineering of the landscape, and increased reliance on a massive and delicately balanced infrastructural network.

The research and images are to be published by the PNAS.