siem reap town – Looking at a satellite image of the Angkor Wat region, it’s hard to miss: straight dark lines show a large canal once ran from the walled city of Angkor Thom about 25 km north to the Kulen hills.
That may mean the Angkorian empire was far bigger than anyone suspected, a spreading collection of houses and small farms similar to the suburbs that sprawl around cities today.
Scientists think the “city” of Angkor covered more than 1,000 square km, which would make it the largest city in the medieval world by a factor of five.
And that vast size may be what killed it, according to Roland Fletcher, a professor at the University of Sydney in Australia.
“We think Angkor Thom was just the core of a much larger urban area,” said Fletcher, who is working with Christophe Pottier of the French School of the Far East. “This was a real monster.”
The team is combining data from traditional archeological digs with satellite and radar images that show large-scale details that had been hidden for years by the forests of Siem Reap province.
Fletcher said Pottier has been doing core drillings within the walls of Angkor Thom, in the city’s heavily-forested southern quadrant. “He has found that it is covered with house mounds and little water [reservoirs] and shrines,” Fletcher said.
The royal palace and temples of Angkor Thom, including the mysterious, many-faced Bayon, appear to have been surrounded by a water-oriented city of orderly streets and canals, terraces and structures made of brick and sandstone.
More than 1,100 small reservoirs as much as three meters deep have been catalogued, along with numerous “hydraulic structures” that may have been canals or sewers.
“We are interested not just in the monuments, but in the urban organization of an ancient city,” said Jacques Gaucher of the Angkor Thom Archeological Research Project. By the end of 2003, he said, all four quadrants of the city should be mapped “and we will know the overall layout of the city in its last state.”
While work on the ground is slow and painstaking—and impossible in many areas north of Angkor Thom, which have not yet been demined—new satellite and radar images indicate the dwellings did not stop at the city walls.
The big northern canal appears to have funneled water from the Kulen hills into a huge network of canals and tributaries stretching about 50 kilometers north and south and 80 kilometers east and west.
“If you had seen Angkor from the air in the 12th century, you would have seen miles and miles of wooden roofs, along roads and canals—a huge, multi-latticed grid, with people living in between,” Fletcher said.
It was not unlike the way people live in rice-growing regions today, he said. However, scientists can’t tell from aerial surveillance whether the fields and terraces they can see on radar are ancient or more recent.
The Angkor area has been aerially surveyed twice, in 1994 from the US space shuttle, and during the 2000 wet season by the US National Aeronautic and Space Administration’s Flying Lab at an altitude of 12,800 meters. Another mission is being planned for December 2003 and January 2004.
Fletcher, an expert on the rise and fall of cities, believes that the huge size of the city of Angkor may be what killed it. Most medieval cities were small and densely populated, but the low-density neighborhoods of Angkor just kept expanding, he believes.
“The implication is that between the 9th and 12th centuries, the Khmer people stripped the whole landscape of trees, building miles and miles of rice fields,” he said.
The fields were fed by irrigation, using the canals and the huge reservoirs as well as natural watercourses, he said. It all worked well until the farmers began to clear land on the upland slopes to the north and west.
“I think it was deforestation” that caused the empire’s sudden collapse, Fletcher said. “They cut too many trees, and that led to higher flooding and more sedimentation in the lake,” as soil washed down from higher elevations into the hydraulic system.
That kind of land use “doesn’t matter much in flat rice lands, but when you get into the hills, it’s a different story.”
He believes the canals and barays filled with silt, holding less and less water, and that finally the Tonle Sap itself became clogged with silt and too shallow to support enough fish.
A sudden drop in the major source of protein would have been a serious enough problem to have caused the rapid collapse of Khmer civilization, Fletcher believes.
The team needs much more data to determine if these theories are true, including archeological dating of features seen from space; a closer look at areas previously hidden by forest; and sedimentation data from the Tonle Sap.
Fletcher says if the theories prove true, the Cambodian government should redouble its efforts to control logging, given the various plans in the region to dam the Mekong River.
“The Khmers engaged in a cycle of ecological and environmental degradation which we may be beginning again,” he said, noting the countries all along the river system want more cropland and more electric power.