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By Root 2027 0

southwest. The direction of flow in one stretch of river was reversed. The big reservoirs were on a modern industrial scale, with in one case banks over 300 feet wide and 30 feet high. The resulting system is so complicated that we are only beginning to understand its operation, and there remain large elements whose function is still a mystery. Obviously, it was designed to manage water, and not just to look pretty and serve as ritual sites, as some archaeologists formerly assumed. The system’s most obvious purpose was for risk management: to smooth out fluctuations in water availability between seasons and years, and to ensure adequate water supply for rice farming even if the monsoon rains should be poor or fail in one year. The system thus served to guarantee the food supply for the capital’s inhabitants, and it illustrates systems used throughout the empire to fuel its population and its power.

By the early 1200s the Khmer Empire under King Jayavarman the Seventh was Southeast Asia’s largest and most powerful state, with its capital at Angkor. In the 1860s the French arrived to find the Khmer kingdom small and weak, with its capital 140 miles south of Angkor at Phnom Penh and only a handful of small villages in Angkor’s former urban area. What happened between the early 1200s and 1860s to produce that result?

A century after Jayavarman the Seventh, the empire underwent a slow decline. While its gold towers and pompous ceremonies still impressed the Chinese visitor Zhou Daguan in 1295-1296, construction of big stone monuments had ceased, the last traditional temple was dedicated in 1295, and the last Sanskrit text was inscribed in 1327. At some time after the early 15th century, new capitals began to develop east and south of Lake Tonle in the vicinity of Phnom Penh, and people seem to have gradually moved away from Angkor. While a Khmer ruler in the 1600s still boasted that he had re-gilded the towers of Angkor Wat, Angkor’s urban area became abandoned after about 1660, and the Khmer kingdom continued to shrink.

One cause of the Khmer decline was the rise of powerful enemies. From the 1200s, both the Thais and the Vietnamese pressed southward, the former on the west from southern China and the latter on the east of Angkor, squeezing the Khmer Empire in a vice. The Thais claimed to have captured Angkor for a while in the 15th century, while the Vietnamese seized the Mekong Delta from the Khmer in the 1700s.

Another cause was a change in the focus of the Khmer economy, from its original inland agricultural emphasis to an increasing involvement in the maritime trade along Southeast Asia’s coast between China, India, and the Islamic heartland. That would have provided a motive for shifting the capital from inland Angkor toward Phnom Penh, with a more direct connection to the coast down the Mekong River. But the Vietnamese expansion later made that Khmer maritime involvement more difficult.

A further big factor that now needs to be added to our understanding of Angkor’s decline is a change in climate. Studies of the water network have yielded seemingly contradictory evidence of both floods and droughts in the 14th and 15th centuries. On the one hand, the big canals to the south of Angkor became filled with coarse-grained sand, implying heavy rains and strong flooding. On the other hand, the exit channels of the big baray were blocked, while the East Baray exit was reconstructed to make it narrower and was then converted from an outlet to an inlet—sure signs of water shortages and attempts to keep the reservoir water levels high. The resolution to this paradoxical combination of floods and droughts has just emerged from publication of a 979-year-long record of tree-ring widths, similar to the tree-ring records that have illuminated climate change in the Anasazi area as I discussed in Chapter 4. These records show that monsoon rainfall in Southeast Asia became much more variable after A.D. 1350, with severe droughts from about 1336 to 1374 and from 1400 to 1425, and exceptionally heavy rainfall in some years between