A not-so-dense idea

Rubina Raja and Søren M Sindbæk on low-density urbanism at ancient sites.

In 1699, the Jesuit missionary Père Joseph Henri Marie de Prémare wrote home from his new quarters in Sumatra, a world still unknown to most Europeans, and difficult for them to grasp: ‘Imagine a forest of coconut trees, bamboos, pineapples, and bananas, through the midst of which passes quite a beautiful river all covered with boats; put in this forest an incredible number of houses made of canes, reeds, and bark, and arrange them in such a manner that they sometimes form streets, sometimes separate quarters: divide these various quarters by meadows and woods: spread throughout this forest as many people as you see in your towns, when they are well populated; you will form a pretty accurate idea of Achen [Aceh] and you will agree that a city of this new style can give pleasure to passing strangers…’ (quoted from Anthony Reid, ‘The structure of cities in South-east Asia, 15th to 17th centuries’).

To many of us, the idea of ancient cities conjures images of a dense maze of buildings, crowded streets, and towering walls. Yet archaeology tells us that urban societies sometimes looked very different from such a strongbox of people. Just how different became apparent to Roland Fletcher at the University of Sydney in the 2000s, when data from remote-sensing instruments in space began to augment archaeology’s eyes.

Unexpected cities

Back in 1994, NASA’s Space Shuttle Endeavour obtained the first radar topography data for selected areas of the world, producing high-resolution elevation maps of the Earth, which were more detailed and comprehensive than any previous topographic mapping. As the data were gradually made public, they revealed unknown archaeological features.

One site that took on a dramatically different look thanks to this eye in the sky was the famous group of temples at Angkor in Cambodia. As Fletcher and his colleagues discovered, the towering 12th-century AD temples, often imagined as a large monastery in the jungle, were surrounded for tens of kilometres ] in every direction by the footprint of a lost, sprawling garden city. With further aerial radar survey by plane in 2000, NASA covered all of greater Angkor, plus an additional 6,000km² of the surrounding region. ‘Greater Angkor’ is today thought to have housed more than half a million inhabitants, making it perhaps the largest settlement anywhere on Earth in its heyday.

What became conspicuous, though, as this urban giant came to be further explored, was that its fabric was made up of endless garden plots, sprinkled with local ‘community centres’ with structures such as small temples or markets, resembling something like an oversize village or a modern suburb without cars. Yet it had clearly maintained many urban functions, including servicing its vast temple institutions. Fletcher named this pattern of settlement ‘low-density urbanism’, a term that has become pivotal to archaeological debates over the last decade.

The temples at Angkor were once thought to be isolated in the jungle. Now, thanks to a range of remote-survey techniques, we know that they lay within a sprawling garden city that may have been home to more than half a million people. Image: © Rodrigolab | Dreamstime 

‘Low-density urbanism’ has been recognised in South-east Asia and Sri Lanka, in Maya settlements, in Celtic Europe, even in Neolithic settlements. It breaks new ground for population estimates, scaling relationships, and patterns of human history. To Fletcher, whose seminal book The Limits of Settlement Growth put settlement studies on a new footing in 1995, they mark an exhilarating discovery, but also a disturbing historical trend. In a much-cited paper in the book Disrupted Balance – Society at Risk in 2018 he notes that ‘low-density’ settlements have often collapsed rapidly, being perhaps less able to respond to environmental change than civilisations based on networks of ‘strongbox’ cities. If so, this is a worrying prospect in a world that is coming today to look ever more like one giant ‘low-density’ city.

There are vast philosophical and historical questions attached to the idea of low-density urbanism, but also formidable technical problems. One is rather obvious: how exactly can archaeologists measure the scale and density of ancient sites? This is a question of methods and scale of investigations. Classic excavations, like Leonard Woolley’s 1920s excavations at Ur, managed to uncover large sections of former townscapes. Yet even these ambitious projects only exposed a limited sample of the site, and often focused on a single period.

Geophysics and remote-sensing have expanded our view considerably, but the results of such surveys can be equally difficult to interpret. In a brand-new study published earlier this year in Antiquity, Augusta McMahon and colleagues used moisture patterns captured in drone-photos after rainstorms to map structures at 3rd-millennium BC Lagash, Iraq. Combining these images with geophysical surveys and excavations, revealed walls, streets, and other architecture, their maps certainly suggest a dense urban site. But how dense is ‘dense’? And how widely did the pattern noted at Lagash extend?

Into the woods

When the concept of low-density urbanism was initially defined, space imagery like the Shuttle Radar Topography data was the pinnacle of detailed spatial data. Now a new generation of airborne high definition LiDAR surveys is setting an even higher standard. This allows settlements to be measured in close detail, even under a dense forest canopy. The results are illustrated by the extraordinary ancient settlements revealed in the Bolivian Amazon by Heiko Prümers and colleagues in Nature in 2022.

More recently, Damien Evans and Roland Fletcher had Angkor mapped again, using similar high resolution methods. The results, which were presented by Sarah Klassen and colleagues in 2021 in Science Advances, suggest that the central area around the temples was much more densely occupied than the vast, surrounding agro-town. Even if there was no exact physical boundary between these two zones, it is now clear that downtown Angkor would have looked more like a dense, traditional city than a low-density suburb. In other words, the density we assess for the population of Angkor depends on how large we consider the functional area of the city to be – a problem of complementarity that would have thrilled the physicist and Nobel Prize-winner Niels Bohr.

A similar situation has been observed by Marcello A Canuto and his colleagues in a LiDAR survey of Maya settlement in Guatemala, published in 2018 in Science. Like Angkor, Canuto’s Maya cities combine large areas of low-density settlement with cores that are much denser. How can we compare such a pattern of settlement with, for example, Classical Athens, which was strictly confined behind city walls?

In 2018, a Danish-German team, who worked for several years in the Decapolis city Gerasa in modern northern Jordan, published a study in PNAS. For the first time in the region, this brought together a string of remotely sensed data, including LiDAR, in order to model the city’s development – both in ancient and modern times. By combining aerial photographs of various vintages with modern airborne laser-scanning, they demonstrated that such data are invaluable for mapping both surviving archaeological features and – when seen over a century-long perspective – also add context for what has been lost. Such studies can heighten awareness of heritage degradation, while also giving information about how a site developed over time, both in recent decades and the distant past. For example, the results showed that large parts of the ancient walled city were left empty in antiquity and used for urban gardening, as another study by some of the team, published in Journal of Archaeological Science: Reports in 2022 showed. This casts new light on aspects to be considered within the spectrum of low density urbanism.

Much as low-density urbanism continues to garner archaeological research results and ideas, it raises the question of how archaeologists define their sites, and what their definitions capture. To Fletcher, the concept implies not just a style of urban layout, but also a particular trajectory over time – something even more difficult to tease out from archaeological data. It is also why such discussions must inevitably range further than current limits of data and ideas – whether dense, or not-so-dense. Progress comes from seeing beyond the trees that make up the forest, which is exactly what remote-sensing helps us to do.

Rubina Raja is professor of classical archaeology and director of the Centre for Urban Network Evolutions, Aarhus University, Denmark. Together with Søren, she is founding editor of the Journal of Urban Archaeology.

Søren M Sindbæk is professor of medieval archaeology at Aarhus University, Denmark, and co-director of the Centre for Urban Network Evolutions.