After resisting Siamese invaders for years, Cambodia's greatest city and civilization -- temple-studded Angkor -- was dealt a death blow with its final sacking in 1431.

Or, so say the history books.

But an international research team now thinks its demise was set much earlier, by something that is the bane of many modern urban societies -- ecological failure and infrastructure breakdown.

"They created ecological problems for themselves and they either didn't see it until it was too late, or they couldn't solve it even when they could see it," said Roland Fletcher, an archaeologist working on the Greater Angkor Project.

Angkor city, the capital of several Hindu kings who ruled over large swaths of Southeast Asia, flourished from the 9th to the 14th centuries, leaving a legacy of architectural splendor in its myriad temples, including the country's cultural icon, Angkor Wat.

Project members are working on the theory that the residents of Angkor created an elaborate system of reservoirs and canals -- for irrigation, trade and travel -- that began to silt up as the population grew, and perhaps caused flooding and water shortages.

Experts say Angkor's demise is important to study because it can provide lessons for dealing with modern urban problems.

Damian Evans, an archaeologist working on the project, said Angkor's canals were the equivalent of today's freeways and our telephone lines are a form of communication that can be equated with the old elephant paths.

"It's the same kinds of problems manifesting themselves in different ways," he said.

Seeking evidence for its theories, the Greater Angkor Project team is excavating waterways and digging up pottery and pollen grains. Members pore over radar ground-images collected by NASA and photographs taken from an ultra-light plane to map the remnants of the ancient civilization, such as rice paddies, houses, shrines and canals.

About 40 people are working on the current phase of the project, a joint effort of the University of Sydney in Australia, the French School of Far East Studies and the Cambodian government's Apsara Authority, which manages Angkor.

In the past, archaeologists focused primarily on studying the intricately carved stone walls of Angkor's temples, which tell stories from Hindu mythology.

The Greater Angkor Project is "essentially a shift from dominantly looking at the churches and cathedrals of a city to looking at housing, drainage, roads -- the daily life stuff," Fletcher said.

Fletcher, a professor at the University of Sydney, theorizes that population pressures and water woes made it harder to trade and communicate. People began migrating south toward the area around what is now the city of Phnom Penh, where subsequent capitals were set up.

The Greater Angkor Project's first goal was to determine how far out Angkor city spread before trying to determine what led to its fall.

They learned that the metropolitan area extended far beyond Angkor Thom, the 700-year-old walled city that houses Angkor Wat. Angkor was home to about 750,000 people and covered about 386 square miles -- much larger than any other preindustrial development and similar to the shape and size of modern cities, Fletcher said.

"It's like a Los Angeles. It's not like Hong Kong," he said. "Lots and lots of open space, big gaps around the houses, huge freeways, which are the canals in this case."

The city's economy was based on rice, and rice paddies spread along dozens of canals, at least one up to 12 miles long. A network of reservoirs, canals and bridges was created to move people and goods and to ensure there was enough water to grow rice.

Angkor engineers even changed the direction that some rivers flowed in what essentially was "a human-built landscape for growing rice," Fletcher said.

The system had three zones: catching water in the north, storage in the center and dispersal in the south. The engineers also created a man-made river to join two natural ones.

As Angkor's population grew, so did the strains on its intricate water system, the scientists say.

"The more modifications they made, the more problems they ran into, and the harder and harder it became to implement solutions to the problems," said Evans, who uses aerial photos, NASA images and on-the-ground investigations to generate a computer map of the water system.

The growing population also forced people to venture into the nearby Kulen hills to cut down trees for fuel and to clear land for growing rice. That would have resulted in rain runoff carrying sediment down into the canal network, Evans said.

"Anything that happened to that water management system would have had a great deal of consequence for all of the people," he said.

There are signs of apparent breaches of and repairs to the water system, although it's hard to tell if they happened during the Angkor era.

"If you think of the freeway and the railway system failing in a modern city -- it's like that," Fletcher said. "It's an infrastructure problem. Everything else might be working fine, but if the infrastructure goes, this thing can't function."

Near the shrine of Prasat Tonle Sngout, near Angkor, researchers discovered evidence of a canal system and wooden structure thought to be a hospital.