Lost cities and disappeared civilizations are an abiding source of fascination for most of us. As Joseph Tainter writes in The Collapse of Complex Civilizations:
Cities buried by drifting sands, or tangled jungle, ruin and desolation where there were people and abundance. Surely few people can read such descriptions and not sense awe and mystery.
Few indeed. And high on that list of lost cities is Angkor Wat, a Cambodian temple complex created during the Khmer Empire, which lasted from the ninth to the fifteenth century. At its peak more than 750,000 people may have lived in Angkor, the region’s capital, but by the time Portuguese missionaries arrived in the late 16th century the empire was tottering and falling.
What happened? There have been many theories, but chief among them was predations from warring invaders, or possibly a shift in trade from land to sea, dooming this inland capital.
A new theory is emerging, however, as a recent National Geographic article says, one that makes the Angkor collapse more Tainter-ian. It seems increasingly likely that the region was made viable by a series of canals and reservoirs, some of which have only begun to be fully understood in recent years. The scope of water engineering has turned out to be immense, with most of the landscape now deemed artificial, the product of engineered hydraulics.
As is so often the case, however, the system became a prisoner of its own complexity. The original system of canals and reservoirs was tied, over time, to new spillways, plus a larger canal and related dam. These show signs of having seen significant stress, perhaps a reservoir going dry, all causing endless repairs to keep this rickety and vast system of waterworks operating.
The preceding was likely survivable, but a complex and coupled system was pushed over the edge. According to recent tree-ring data, the region was hit by repeated mega-droughts, from 1362 to 1392 and again from 1415 to 1440. There were severe droughts followed by mega-downpours, likely causing food stresses, and even wiping out big chunks of the Angkor waterworks — and ultimately the Khmers at Angkor themselves.