Collapse_ How Societies Choose to Fail or Succeed - Jared Diamond [338]
We can now place Angkor’s decline within the framework of the five sets of factors that I proposed in this book’s prologue for understanding a society’s success or failure. First, the Khmer did inflict unintentional damage on their environment: they deforested the Angkor plain and the slopes of the Kulen Hills. Without trees to slow rain runoff, heavy monsoons eroded soil and dislodged sediment that was swept into canals, and floods incised the Siem Riep River’s channel. That river is now about 20 feet below the Angkorian land surface. Second, climate change exposed the Angkor area to conditions both drier and wetter than Angkor’s system was designed to accommodate. Third, the Khmer, like the Roman Empire and the Greenland Norse, faced growing problems from hostile neighbors. Fourth, friendly trade partners played a role, by offering the Khmer maritime economic opportunities more attractive than the inland opportunities available at Angkor, but then those opportunities became restricted. Finally, the Khmer Empire responded to the attractions and the problems of the Angkor environment by becoming committed to an increasingly huge, complex, and hard-to-maintain water management system from which there was no going back. All five of those factors interacted: climate change and erosion weakened the Khmer to the point where they could no longer resist their enemies, no longer maintain and improve their water management system, and turned away from an agricultural economy to maritime trade until shifting trade routes and political power made that, too, less profitable.
We can also place the Khmer decline within the spectrum of collapses, from quick and lethal to slow and non-lethal. At the former extreme lies the end of Greenland’s Western Settlement, where everybody may have died in a single winter. Angkor’s decline seems to lie toward the opposite extreme: it extended over centuries, people gradually moved away, and there is no evidence of massive die-offs of people. But the result, nevertheless, was unequivocally a collapse: scattered villages in the former metropolitan heartland, on the site of what once had been a world-class city and the capital of the region’s most powerful empire.
For all of us fascinated by the glory and the mystery of Angkor, these are exciting times. We have gained much detailed knowledge about the city in the last decade, building on the previous century of archaeological investigation. But big questions remain unsolved, and the next decade promises to be even more exciting. Here is my short list of five sets of questions to which I would love to know the answers by the year 2020:
Where did Angkor’s population get its wood for construction and fuel? The city’s 750,000 people must have needed huge quantities of wood for building houses and other structures, and to make charcoal for cooking. Yet the original forest of the Angkor plains and much of the Kulen Hills was cut down, and it boggles the mind to imagine that the trees then planted by people around their houses could have met the needs of such a large population.
How did the Khmer manage water? They surely had methods for recording the monsoons and predicting the resulting water flows. What roles did the shrines in the middle of the baray play in managing the canal network? How did the Khmer move water around the landscape without pumps? The West Baray was not dug into the ground but was built on the ground, and cleverly positioned so that the intake canals provided a water surface several feet above ground level at the exit. How did Khmer water engineers shift water flows from one channel to another as needed? Did the canals have movable gates?
How did the whole water management system function? It includes many big structures that have been located but whose purpose remains unknown.
Why has it taken so long for Angkor to regain its formerly dense human population,