Ancient capital cities often grew for centuries, reached a Golden Age, and then collapsed rapidly:
Angkor was flourishing in the late 13th century when Zhou Daguan visited; a little over a century later, it was all but abandoned. Researchers are beginning to see similarities in how these ancient low-density cities failed — and this is of particular interest today because, even as our cities grow in extent and population, their densities are falling.
There had long been a debate about what led to the decline of Angkor and the southward move of the Khmer seat of power. Proposed explanations included the strain on theocratic rule of Hindu-Buddhist jostling; attacks by Thai armies; and changes brought about by maritime trade. But the Greater Angkor Project added a significant new possibility: extreme climate instability. Analysis of tree rings in neighbouring Vietnam showed long periods of droughts followed by periods of unusually wet monsoons in the 14th and 15th centuries.
The upheaval caused by flooding during mega-monsoons is clearly visible in remote sensing images produced by the project: erosion channels show rapidly moving water breaching a dam, crashing into the wall of a reservoir, then tearing away the edge of a residential area, flowing at a high level through housing, and later damaging a bridge. Perhaps the scenes in Angkor were not very different from those seen in recent years in New Orleans or Fukushima.
Sand accumulated in Angkor’s canals, and parts of the water network were cut off from each other. Damage to an old, complex water management system meant the city became less resilient in intervening periods of drought. Angkor, with its large population and broken infrastructure, would have found it hard to sustain itself.
The pattern of urbanism at Angkor was hardly unique: the Mayan cities that Pottier’s maps of Angkor reminded Fletcher of have long been recognised as low-density agrarian settlements. The lack of the wheel and the absence of draught animals meant that large quantities of food could not be transported, and cities had to be largely self-sufficient, growing maize, varieties of beans, squash, manioc and other staples of the region.
The city of Tikal, in present-day Guatemala, was one of the most important of these Mayan centres. In what is called its Late Classic Period, around 600 AD, there was a flowering of art and architecture: large plazas, palaces, pyramid temples, sculpture and painted ceramics (of the many structures still found in Tikal, a 65-metre high pyramid is one of the tallest man-made structures in all pre-Columbian America). Conservative estimates put the city’s population at around 45,000 during this period; the city extended over 160 square kilometres. Then, in the middle of the ninth century, Tikal collapsed.
Originally, the area of Tikal was around 70% upland tropical rainforest, and the rest swampy wetland. An extended family would build their houses in a cluster, with cultivable land attached. In all, the people of Tikal cleared around two-thirds of the rainforest to create their monuments and homes, and to fuel their fires. “In many ways they were managing the forest very effectively,” says Lentz. “But they weren’t aware that cutting down a forest reduces the amount of precipitation in the region. Then suddenly a horrible drought comes along, and they can’t figure out why they can’t supplicate their gods adequately to prevent it.”
It didn’t help that Tikal’s water management system had become increasingly reliant on collecting rainwater in reservoirs, at the cost of groundwater. “As Tikal grew and grew,” Lentz says, “they created all these pavements around the city, from which they’d divert water to the reservoirs. But this cut off the recharge capacity of the springs. When there was no longer any rainfall to fill up their reservoirs, the springs had dried up too.”
For centuries, the Maya at Tikal had been erecting stelae — upright stone slabs with hieroglyphs and depictions of gods and rulers. The last one is dated 869. Soon after, there are signs of what might today be called urban decay, with palaces being occupied by squatters. Charred, gnawed human bones from this late period suggest desperate times. Then, the city went quiet.
Lentz draws a comparison with a neighbouring city called El Zotz, which had a smaller population, which didn’t modify its landscape as drastically, and was thus able to survive the drought that felled Tikal.
Tikal, Angkor and Anuradhapura (which foundered in the 10th century after thriving for more than a millennium) were very different cities in their geography, environment and social and political functioning. But, Fletcher points out, they all had operational similarities: extensive land clearance, sprawling low-density settlement patterns, massive infrastructure — all of which are attributes of modern cities. The extended infrastructure of Angkor and Tikal proved vulnerable to a changing climate, something else that may be upon us.