Aerial radar sizes up ancient urban sprawl

Laser pulses beamed from a low-flying airplane into northwestern Cambodia’s dense jungles have revealed ancient remnants of extensive, carefully planned settlements of rice farmers. These settlements were part of Angkor, the capital of the region’s Khmer empire.

Angkor flourished from around 900 to 1500, but forests now obscure much of the city’s urban sprawl. Laser technology called lidar has now seen through the jungle to the ground. It shows that, starting around 1100, roadways and canals formed rectangular grids — much like modern city blocks — around Angkor’s central temples and royal palaces, say archaeologist Damian Evans of the University of Sydney and his colleagues. Similar grids containing villages, ponds and small temples spread out far into the countryside over the next few centuries, covering as many as 1,000 square kilometers, the researchers report June 17 in the Proceedings of the National Academy of Sciences.

New probes of Angkor’s landscape support an increasingly popular idea: The city grew so large that its canals and reservoirs could not provide enough water when severe droughts hit around 1400. Residents may have gradually abandoned Angkor for cities built near rivers, in the region of today’s Phnom Penh.