How big were the world’s ancient cities? At its height, the world’s first city of Uruk may have had about 40,000 people about 5,000 years ago. In the medieval period, London may have had a population of about a quarter of a million people, growing to approximately 600,000 by the early 17th century.
One of the world’s largest ancient cities lay in the jungles of Southeast Asia in the greater Angkor region located in contemporary Cambodia. This medieval site was home to the Angkor or Khmer Empire from the ninth to 15th centuries. You might be familiar with the famous Angkorian temple, Angkor Wat, one of the largest religious monuments in the world.
But most people don’t realize that Angkor Wat is just one of more than a thousand temples in the greater Angkor region. Our research suggests that this settlement may have been home to between 700,000 and 900,000 people at its height in the 13th century. This means that the population of Angkor was roughly comparable to the almost 1 million people who lived in ancient Rome at its height.
Here’s how our interdisciplinary team came up with our population estimate for Angkor and how it grew over time.
Over the last 30 years, archaeologists working in collaboration with Cambodia’s APSARA Authority have been exploring the jungles and rice fields of Cambodia, documenting thousands of medieval features that remain inscribed on the landscape. This work has included digging traditional excavation sites, surveying the landscape from the back of dirt bikes and scanning satellite imagery for traces of these ancient features.
Our knowledge of the region entered a new era in 2012, when researchers from the Khmer Archaeological Lidar Consortium organized a mission of airborne-laser scanning across this World Heritage site. Called lidar, this technology was able to do in a few days of scanning and data-processing what had previously taken archaeologists months if not years of work: see through dense vegetation to accurately map the ground surface of Angkor.
With this lidar data, researchers were able to map tens of thousands of archaeological features at Angkor. Because Angkorian people, like many Cambodians today, built their houses out of organic materials and on wooden posts, these structures are long gone and not visible on the landscape. But lidar revealed a complex urban landscape complete with city blocks consisting of the mounds where people built their houses and small ponds located next to them.
This work has created one of the most comprehensive maps of a sprawling medieval city in the world, leading us to ask: How did the city develop over time, and how many people lived here?
Deducing who used these structures and how
Our new research published in the journal Science Advances created a comprehensive database that unites 2012 lidar mapping work with a massive archaeological data set acquired by an international team of scholars over the last 30 years. Our goal was to combine all available data into one framework so we could understand which buildings had existed at various points in time and then ascribe the right number of people to each structure in order to come up with overall population estimates.