On an arc of land between the Mediterranean Sea and the Persian Gulf sits the birthplace of cities.
It's sometimes referred to as "the Cradle of Civilization," but it's more widely known as the Fertile Crescent. And fertile it was. The flowing Tigris and Euphrates rivers created rich agricultural opportunities for early humans, who settled in city-like structures as early as 4000 BC.
Archaeologists have excavated extensive portions of the Fertile Cresent, but they've long been in the dark about what the world's first cities looked like, and why they came about.
Not anymore. Researchers at Harvard University have developed a technique to comprehensively identify the settlements that developed and faded away here over the last 6,000 years. This research has created a more complete picture of early urbanization.
A false-color satellite image (left) of the area near modern-day Hamoukar, Syria. The black outlines in the image on the right indicate likely ancient settlement sites.
By analyzing satellite imagery, archaeologist Jason Ur and computer scientist Bjoern Menze have identified thousands of settlement sites in one section of the Fertile Crescent. They've mapped more than 14,000 settlement sites in a 23,000-square-kilometer region in northeastern Syria, and they suggest that their method can be used to map the entire region. Their work appears in this month's Proceedings of the National Academy of Sciences.
Ur and Menze trained a computer program to analyze the satellite imagery's pixels to detect large concentrations of "anthropogenic sediments" – the remains of buildings and settlements now turned to dust, mounding up from the alluvial basin of this part of Syria, and detectable through radiation from the near infrared and infrared spectrum.
"One of the conclusions that we've drawn – and this won't be a terrible shocker – is settlements that were closer to perennial water sources or in areas of higher rainfall tended to have longer life histories, they tended to be larger in volume," says Ur.
But not every early civilization made straightforward resource-based decisions about where to settle. A fairly significant amount of the settlements he and Menze identified were not necessarily near water or other natural benefits.
One example is Tell Brak, a mound of about 8 million cubic meters in volume and about 40 meters in height. It's one of the largest tells, or ruin mounds, in the Fertile Crescent, but it’s also located a few miles from the nearest stream.
The Tell Brak mound in northeastern Syria.
"This is really interesting to us because it shows that these very simplistic, environmentally-driven models for where people should live long term can fail very clearly when places develop a meaning that goes beyond this environmental determinism," Ur says. "Clearly this place had some cultural meaning, some cultural significance that we don’t fully understand."
Ur hypothesizes that such places grew in prominence over time because ancient people had some sort of long-term connection, possibly due to ancestry. But it also could be that people were drawn to places others had already settled. For a modern-day analog, Ur points to Chicago.
"Chicago took its place because it was close to Lake Michigan and the Mississippi," Ur says. "However, technology has evolved to the point where that position doesn’t really matter any more ... It became a significant place in and of itself, independent of its location."
This new map also challenges previous ideas that the earliest cities were official constructs, created by kings or rulers. Ur says that places like Tell Brak show that early urbanization developed organically.
"We're talking about 6,000 years of urban development in one place. And cities change through time. This is one thing that’s really emerging from intensive research that’s been done in the last ten years: there's no one model for the city," says Ur. "There are any number of different approaches."