Using archaeological excavation data, historical reports and maps, and modern laser scanning results, researchers have modeled the growth of the historic city of Angkor in what is now Cambodia. The calculations show that the various areas of the metropolis have developed at different speeds over the centuries. At its heyday in the 13th century, the city had between 700,000 and 900,000 inhabitants, according to researchers.
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. Non-religious buildings in Angkor, however, were less durable: Constructed from organic materials, they crumbled long ago. That makes it difficult to estimate the population of the former metropolis. Therefore, although Angkor is one of the largest premodern cities in the world, important information regarding the population and its development has so far been missing.
Extensive data combined
A team led by Sarah Klassen from the University of British Columbia in Canada has now filled this knowledge gap. “Estimating Angkor’s population is an ongoing challenge,” the researchers write. Having no residential buildings or similar infrastructure as a reference point, they focused on subtle traces of the crumbling urban environment. They collected extensive data from 30 years of research in the form of archaeological excavations, historical reports and maps and modern lidar measurements, in which an area is scanned from the air by laser. Using machine learning methods, classes and their colleagues created a model that depicts the development of the entire 3000 square kilometer metropolitan region around Angkor.
From the model, the researchers can deduce how the population developed between the seventh and thirteenth centuries. They differentiate between the central region, in which the royal residence and the stone temples were located, the extended urban area and the dams along the irrigation system. “It took the population of Angkor several centuries to peak after it was founded,” the authors report. It is noteworthy that the population growth in the different areas of Angkor took place at different speeds.
Population growth thanks to the irrigation system
While the center, urban area and dams recorded similar population increases in the earliest phase, the number of people in the urban area had already quadrupled by the tenth century, probably due to increased investment in infrastructure. The center, on the other hand, did not begin to expand rapidly until the eleventh century. The metropolis of Angkor reached its heyday in the 13th century. “Our model shows that between 700,000 and 900,000 people lived in the metropolitan region at that time,” the researchers report. In the center, the population density at that time was up to 7500 inhabitants per square kilometer.
An important basis for this was a sophisticated water supply for the city. “The elites in the central zone developed an extensive water management and transport infrastructure that included large parts of the landscape and enabled the population to grow,” the researchers explain. However, shortly after this heyday, Angkor began to decline. “Scientists have pointed out the fragility of such expensive urban systems,” the authors write. “However, recent work suggests that the Angkor region was not completely depopulated.”
Nuanced approach to demographic analysis
Their method of estimating population development can also be applied to other historic cities, the researchers write. It is important to differentiate between the different settlement areas. “In this way, we offer a nuanced approach to demographic analysis that takes into account variations in population density depending on the area,” the authors say. “For example, we found that the center and the extended urban area of Angkor developed at different times and independently of one another.” Future studies could show the extent to which such dynamics also existed in other historic cities around the world.
Source: Sarah Klassen (University of British Columbia, Canada) et al., Science Advances, doi: 10.1126 / sciadv.abf8441