The ancient Khmer city of Angkor in Cambodia was the largest preindustrial metropolis in the world, with a population near 1 million and an urban sprawl that stretched over an area similar to modern-day Los Angeles, researchers reported Monday.

The city's spread over an area of more than 115 square miles was made possible by a sophisticated technology for managing and harvesting water for use during the dry season -- including diverting a major river through the heart of the city.

But that reliance on water led to the city's collapse in the 1500s as overpopulation and deforestation filled the canals with sediment, overwhelming the city's ability to maintain the system, according to the report in the Proceedings of the National Academy of Sciences.