Using archaeological excavation data, historical reports and maps, and recent laser scanning results, the researchers modeled the growth of the historic city of Angkor in what is now Cambodia. Accounts show that different areas of the city developed at different speeds over the centuries. According to researchers, at its height in the thirteenth century, the population of the city was between 700,000 and 900,000.
Angkor, the former center of the Khmer Empire, is world famous for its temple complexes, including Angkor Wat, the largest preserved temple complex in the world. However, secular buildings in Angkor were less durable: constructed from organic materials, they had been repaired a long time ago. This makes it difficult to estimate the population of the former capital. Therefore, although Angkor is one of the largest pre-modern cities in the world, important information regarding population and its development has been missing so far.
Comprehensive data combined
A team led by Sarah Clasen of the University of British Columbia in Canada is filling this knowledge gap. “Estimating the population of Angkor is an ongoing challenge,” the researchers wrote. Since there were no apartment buildings or similar infrastructure as a point of reference, they focused on the subtle effects of the dilapidated urban environment. They have collected extensive data from 30 years of research in the form of archaeological excavations, historical reports, maps, and recent lidar measurements, in which an area of the air is scanned with a laser. Using machine learning methods, the classroom and their colleagues created a model that depicted the development of the entire 3,000 square kilometer urban area around Angkor.
From the model, researchers can infer how the population developed between the seventh and thirteenth centuries. It differentiates between the central region, where the royal residence and stone temples are located, and the sprawling urban area and dams along the irrigation system. “It took the people of Angkor several centuries to reach their peak after its founding,” the authors say. It is noteworthy that the population growth in the different regions of Angkor occurred at different speeds.
Population growth thanks to the irrigation system
While the center, urban area, and dams recorded similar population increases in the first stage, the urban area population had already quadrupled by the 10th century, possibly due to increased investment in infrastructure. On the other hand, the center did not begin to expand rapidly until the eleventh century. Angkor reached its zenith in the thirteenth century. “Our model shows that between 700,000 and 900,000 people were living in the metropolitan area at that time,” the researchers said. In the center, the population density at that time was 7,500 people per square kilometer.
The important basis for this was the advanced water supply to the city. “The elites in the central region have developed an extensive infrastructure for water and transportation management that encompasses large parts of the landscape and enabled the population to grow,” the researchers explained. However, soon after this peak, Angkor began to decline. The authors write: “Scientists point to the fragility of such expensive urban systems.” “However, recent work indicates that the Angkor region has not been completely evacuated.”
A rigorous approach to demographic analysis
The researchers wrote that their method of estimating population development could also be applied to other historic cities. It is important to differentiate between the different settlement areas. “In this way, we present a rigorous demographic analysis approach that takes into account differences in population density depending on the region,” the authors say. “For example, we found that the center and the sprawling urban area of Angkor developed at different times and independently of each other.” Future studies could show the extent to which such dynamics also exist in other historic cities around the world.
Cowell: Sarah Clasen (University of British Columbia, Canada) et al., Science Advance, Doi: 10.1126 / sciadv.abf8441