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Get the most interesting and important stories from the University of Pittsburgh.People pack up their apartments and leave the city, headed for the suburbs or beyond, for any number of reasons. But when it comes to the failures of some of history’s most impressive cities, researchers often look to catastrophe to understand their drastic downturns.
Experts have long-suspected climate volatility played a starring role in the demises of urban centers across the globe, from Angkor Wat in present-day Cambodia to Cahokia in present-day Illinois. The collapse of Maya cities, which reached their peak during the Late Classic between roughly 600 and 750 CE, is also an often-cited example of climate-driven breakdown.
Although there are still millions of Maya today, by 900 CE, Classic Maya cities throughout southeastern Mexico, Guatemala, Belize and western areas of Honduras and El Salvador were effectively gone.
To better understand what happed to those ancient cities — and what it might mean for our modern cities — a team of researchers, including Claire Ebert, assistant professor in the Kenneth P. Dietrich School of Arts and Sciences’ Department of Anthropology, set out to understand how several factors influenced the rise of Maya cities, as well as their declines.
Ebert worked with a multi-institutional team of researchers who combined archaeological evidence, hieroglyphic records and paleoclimate data to explore how Maya cities responded to environmental and political change. Their results, published in the Proceedings of the National Academies of Science, show correlations between conflict, climate change and cycles of growth and decline in urban areas.
“It’s quite complex,” Ebert said. “The abandonment of cities was not necessarily because there was a big drought and everybody left. Cities don’t just rise and decline simply because it’s wet or it’s dry.”
A leading theory about the demise of these Maya cities has to do with climate, according to Ebert, with many researchers suggesting that drought strained agriculture, which in turn fueled conflict and hardship, eventually leading to a downfall.
A fuller picture required a broader investigation. “We were interested in understanding why cities emerged, rather than just when they disintegrated,” Ebert said. “Are there correlations between the development of cities and their institutions in addition to their demise?”
Charting the rise and decline of a civilization 1500 years later is not a straightforward task. To reconstruct the rhythms of ancient Maya cities, researchers combined evidence from multiple sources: hieroglyphic records that document royal events and wars, archaeological data on population size and agricultural production, and paleoclimate data from lake sediments and cave formations that track rainfall over centuries.
Ebert supplied radiocarbon dating information from across the region, placing structures like canals, reservoirs and agricultural terraces in time. These data also served as a proxy for population size, as more radiocarbon dates generally correspond to periods of greater human activity. The data came from the Mesoamerican Radiocarbon (MesoRAD) database, a collection of thousands of datapoints from the published scientific literature that Ebert developed with colleagues. “We were able to extract data specifically about agricultural infrastructure to understand when these features were constructed and the frequency of construction over time,” Ebert said.
After putting all of the evidence together, the team found no clear-cut, linear relationship between climate and the viability of cities.
“Radiocarbon dates give us a powerful way to track human activity through time,” Ebert said. “By looking at when people were building things like terraces, canals and reservoirs, we can see broader patterns of growth and decline. When we compared those timelines with records of climate and conflict, it became clear that cities and their infrastructure didn’t simply rise and fall with changes in rainfall — social and political factors played an equally important role.”
The researchers’ model shows that during earlier droughts, populations became concentrated around cities with reliable water management systems and political power. People came together to live in cities because the trade-offs were better than trying to go it alone.
“Then we start to see the cities disintegrate in a way we didn’t necessarily expect,” she said. It wasn’t when things got climatically worse, but when rainfall later returned and conditions improved, people no longer needed to depend on those centralized systems. “A wetter environment was productive enough for city dwellers to move back to rural areas.”
There are fundamental differences between ancient and modern cities but understanding the factors that influenced how cities grew and changed may still provide guidance moving forward.
“We can peer into the futures of ancient cities and see the process play out,” Ebert said. The research doesn’t suggest that modern cities should — or even could — mirror those of the ancient Maya, but studying such long-term histories helps archaeologists identify the factors that shaped resilience and transformation.
For example, a modern city may not have terraced agriculture, but it still depends on different types of infrastructure. “All cities have infrastructure,” Ebert said. “The key questions are: when do those systems develop, when they start to break down and why?”
By examining the full trajectory of Maya cities, Ebert said researchers can better understand how communities respond to change and what lessons might guide more sustainable decisions today.
Photography courtesy of Claire Ebert