Ancient cities provide key datasets for urban planning, policy and predictions in the Anthropocene

A new study led by authors from the Max Planck Institute of Geoanthropology, published in the first edition of the new journal Nature Cities, shows how state-of-the-art methods and perspectives from archaeology, history, and palaeoecology are shedding new light on 5,500 years of urban life.

Cities play a key role in climate change and biodiversity and are one of the most recognizable features of the Anthropocene.

They also accelerate innovation and shape social networks, while perpetuating and intensifying inequalities.

Today over half of all humanity lives in cities, a threshold which will rise to nearly 70% by the mid-21st century.

Yet despite their importance for the Anthropocene, cities are not a recent phenomenon.

In a new study, an interdisciplinary team of authors from the Max Planck Institute of Geoanthropology argue that the history of urbanism provides an important resource for understanding where our contemporary urban challenges come from, as well as how we might begin to address them.

The paper highlights the ways in which new methodologies are changing our understanding of past cities and providing a reference for urban societies navigating the intensifying climatic extremes of the 21st century.

These methods range from remote sensing techniques like LiDAR, which are documenting cities in places where urban life was once considered impossible, to biomolecular approaches like isotope analysis, which can provide insights into how cities have shaped different organisms and influenced human mobility and connectivity through time.

Meanwhile, the study of sediment cores and historical data can show how cities have placed adaptive pressures on different landscapes and human societies -- as they still do today.

As understanding of humanity's influence on the Earth system grows, urbanism is increasingly considered one of the most impactful forms of land use.

In this new study, the authors also highlight how multidisciplinary approaches, including Earth system modelling, are revealing the impacts that ancient and historical forms of urbanism had on land use, and, critically, how they compare to the impacts of urban areas today.

Throughout, the authors emphasize that the past does not just provide anecdotal insights, but rather numerical datasets of things like road lengths, building types, population sizes, economic output, environmental impacts, and more.

With advances in computational archaeology, this opens up the possibility of quantifying similarities and differences in urban pathways across space and time, directly linking the past to the present.

By reviewing diverse examples from around the world ranging from medieval Constantinople (now Istanbul) to 9th century Bagdad, from Great Zimbabwe to Greater Angkor in Cambodia, this new study highlights the potential of new methodological approaches to reveal historical legacies and predict trajectories of urbanism in the Anthropocene epoch.

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Archaeologists reveal pre-Hispanic cities in Bolivia with laser technology

More than 20 years ago, Dr. Heiko Prümers from the German Archaeological Institute and Prof. Dr. Carla Jaimes Betancourt from the University of Bonn, at that time a student in La Paz, began archaeological excavations on two "mounds" near the village of Casarabe in Bolivia. The Mojos Plains is a southwestern fringe of the Amazon region. Even though the savannah plain, which flooded several months a year during rainy season, does not encourage permanent settlement, there are still many visible traces of the time before Spanish colonization at the beginning of the 16th century. Next to the "mounds," these traces include mainly causeways and canals that often lead for kilometers in a dead straight line across the savannahs.

"This indicated a relatively dense settlement in pre-Hispanic times. Our goal was to conduct basic research and trace the settlements and life there," says Heiko Prümers. In earlier studies, the researchers already found that the Casarabe culture -- named after the nearby village -- dates to the period between 500 and 1400 AD and, according to current knowledge, extended over a region of around 16,000 square kilometers. The "mounds" turned out to be eroded pyramid stumps and platform buildings.

Initial conventional surveys revealed a terraced core area, a ditch-wall enclosing the site, and canals. In addition, it became apparent that some of these pre-Hispanic settlements were enormous in size. "However, the dense vegetation under which these settlements were located prevented us from seeing the structural details of the monumental mounds and their surroundings," says Carla Jaimes Betancourt from the Department for the Anthropology of the Americas at the University of Bonn.

LIDAR technology used in the Amazon for the first time

To find out more, the researchers used the airborne laser technology LIDAR (Light Detection and Ranging) for the first time in the Amazon region. This involves surveying the terrain with a laser scanner attached to a helicopter, small aircraft or drone that transmits around 1.5 million laser pulses per second. In a subsequent evaluation step, the vegetation is digitally removed creating a digital model of the earth's surface, which can also be displayed as a 3D image. "The first results were excellent and showed how effective the technology was even in dense rainforest. From that moment on, the desire arose to map the large settlements of the Casarabe culture using LIDAR technology," says study leader Dr. Heiko Prümers.

For the current study, in 2019 the team together with Prof. Dr. José Iriarte and Mark Robinson from the University of Exeter, mapped a total of 200 square kilometers of the Casarabe cultural area. The evaluation done by the company ArcTron3 held a surprise. What came to light were two remarkably large sites of 147 hectares and 315 hectares in a dense four-tiered settlement system. "With a north-south extension of 1.5 kilometers and an east-west extension of about one kilometer, the largest site found so far is as large as Bonn was in the 17th century," says co-author Prof. Dr. Carla Jaimes Betancourt.

It is not yet possible to estimate how many people lived there. "However, the layout of the settlement itself tells us that planners and many active hands were at work here," says Heiko Prümers. Modifications made to the settlement, for example the expansion of the rampart-ditch system, also speak to a reasonable increase in population. "For the first time, we can refer to pre-Hispanic urbanism in the Amazon and show the map of the Cotoca site, the largest settlement of the Casarabe culture known to us so far," Prümers emphasizes. In other parts of the world similar agrarian cities with low population densities had already been found.

LIDAR shows anthropogenically altered landscape

LIDAR mapping reveals the architecture of the settlement's large squares. Stepped platforms topped by U-shaped structures, rectangular platform mounds, and conical pyramids (up to 22 meters high). Causeway-like paths and canals connect the individual settlements and indicate a tight social fabric. At least one other settlement can be found within five kilometers of each of the settlements known today. "So the entire region was densely settled, a pattern that overturns all previous ideas," says Carla James Betancourt, who is a member of the Transdisciplinary Research Area "Present Pasts" at the University of Bonn.

The researchers emphasize that for all the euphoria about the site mappings and the possibilities they offer for reinterpreting the settlements in their geographic setting, the real archaeological work is just beginning. The goal for the future, they say, is to understand how these large regional centers functioned.

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