Portion of mural by Diego Rivera showing the Aztec city of Tenochtitlan, photograph by Wolfgang Sauber. This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported, 2.5 Generic, 2.0 Generic, and 1.0 Generic license.

North America’s first cities developed long before the Spaniards set foot in the New World. Surprisingly, they were markedly similar to European cities. Indeed, in 1519 conquistador Hernán Cortés wrote his king about how familiar the scene was in Tenochtitlán, the capital city of the Aztecs and what is now Mexico City.

A new analysis led by researchers at the Santa Fe Institute and the University of Colorado Boulder suggests that these similarities arise from general, universal growth mechanisms that govern the development of all human settlements, from the ancient cities of the Toltecs and Aztecs to modern megacities today. In a February 12 paper in PLOS ONE, they present a set of equations that describe these growth patterns.

Read the paper in PLOS ONE (February 12, 2014)

“People need to interact in order to trade, to divide labor, to share information,” says SFI Professor Luis Bettencourt, a physicist. “Cities solve this universal problem by concentrating social networks in space.”

But how do people accomplish such concentrated interaction in practical terms? Bettencourt has long studied that question as it relates to modern cities, analyzing vast amounts of urban data and deriving a series of mathematical formulas that zero in on the ways human groups create cities themselves – as opposed to how rulers and planners have long believed them to grow.

In contrast Scott Ortman, a former SFI Omidyar Fellow who is now a professor of anthropology at Boulder, has focused on reconstructing ancient settlement patterns using archaeological data to better understand how human societies respond to social, technological, and environmental change.

In their paper, Ortman and Bettencourt join forces to determine whether the patterns and processes observed in contemporary cities are reflected in the archaeological record of one of the world’s great early civilizations.

Working with collaborators Jennie Sturm (University of New Mexico) and Andrew Cabaniss (University of North Carolina – Chapel Hill), Ortman and Bettencourt figured out how to translate the concepts developed for modern cities to ancient settlements, applying these new ideas to data recorded in an archaeological survey of the Valley of Mexico in the 1960s – before the expansion of Mexico City destroyed many of the ancient settlements.

“By working together, we hit upon something neither of us could have recognized on our own,” Ortman says. “The implications are potentially profound.”

Bettencourt's work suggests modern cities become more efficient spatially as their populations grow, and that these economies of scale emerge from individuals balancing the costs of moving around with the benefits of the resulting social interactions. As these are general properties of human social networks regardless of the context, Ortman reasoned this theory could be tested by applying it to archaeological data.

Using information from more than 1,500 ancient settlements spanning more than two thousand years and four major cultural periods, the team developed a number of predictions from their scaling models. They then showed that the ancient settlement patterns of the Valley of Mexico not only met these expectations, but exhibit the same relative mathematical scaling properties observed in modern cities.

Their findings help validate the models derived for modern cities and suggest that the scaling principles may apply to the entire range of human history, regardless of how far apart settlements might be in time, space, or culture.

“Our study suggests that contemporary cities lie on a continuum with the earliest human settlements,” Ortman says. “If that is so, the same models – which are ultimately governed by human interactions – can serve as new tools for gaining insights into how cities emerged in the first place.”

This link between ancient and modern cities also has significant implications for the future, notes Bettencourt, as humans are fast becoming an urban species.

“It is cities, rather than villages or rural towns, that are the fundamental socioeconomic unit in the world today,” he says. “Without good models for understanding how they work and the benefits they provide, it's very hard to understand the role of cities in the history of civilization or to figure out what ancient cities can teach us about our present urban centers.

“We've long lacked a model that can accurately explain how cities around the world work – both today and in the distant past,” adds Ortman. “Here we provide a bridge.”

Read the article in Archeology magazine (April 8, 2014)

Read the article in Time magazine (February 25, 2014)

Read the article in Smithsonian (February 14, 2014)

Read the post in the PLOS community blog (February 21, 2014)

Read the post in Michael E. Smith's Publishing Archeology blog (February 16, 2014)

Read the University of Colorado Boulder news release (February 12, 2014)

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