Tony Wilkinson, research associate at the university's Oriental Institute, said the ancient roads lost favor when better routes were established. The 5,000-year-old roads, between 200- and 400-feet wide and 20- to 24-inches deep, were in depressions and later became sources for moist clay to make mud bricks for building.
The scholars concentrated on the northern section of Mesopotamia but said such road systems likely were common throughout the Near East.
"When considered at a regional level, these routes emerge as segments of larger 'highways' that run from site to site on a generally east-west axis," wrote Jason Ur, a researcher at the institute, in his paper, "CORONA Satellite Photography and Ancient Road Networks: A Northern Mesopotamian Case Study," to be published in the spring issue of the journal Antiquity.
Archaeologists always assumed roads existed between major settlements but the imagery for the first time has shown them the precise locations.
Ur said the data lend credence to suppositions archaeologists have long made.
"Using declassified intelligence information, we can now map large scale landscape features we've never been able to see but have inferred by drawing lines between ancient sites. We can actually map them using traces of their remains," Ur told United Press International.
The roads indicate some urban centers grew to massive size and relied on intensive agriculture in surrounding fields to support that growth.
Unlike the so-called Cradle of Civilization in southern Mesopotamia where agriculture was dependent on irrigation, the area Ur and his team studied in northern Mesopotamia had a climate much like the Midwest, dependent on rain for crops to grow.
Former Army satellite imagery interpreter Jennifer Pournelle, co-director of the Mesopotamian Alluvium at the University of California-San Diego, said what we see in these Cold War images is "the end of Eden."
Pournelle said the road system extended over southeastern Turkey, northern Syria and northern Iraq, "three areas we now think of as unstable and politically divided."
"The routes are still there. ... If we can get a little bit of stability, the area will thrive again," she said.
The Oriental Institute has been concentrating much of its research on the Syrian sites of Tell Brak and Tell Hamoukar. The satellite images show Tell Hamoukar was more important than scholars previously had thought and likely was part of a road system that stretched from Nineveh in modern Iraq to Aleppo in western Syria, Wilkinson and Ur said.
"For the Early Bronze Age, new conclusions can be drawn about the underlying economy, which had a large role in producing this pattern of settlements and roads," Ur said. "The agricultural backbone of these towns is vividly illustrated by the abundant radial system of roads, although the interconnectedness of these systems suggests a far more integrated agricultural economy than originally recognized."
High-value luxury goods, such as textiles and metals, also traveled these routes.
The roads fell out of favor in a general collapse of the urban civilization at the end of the third millennium B.C., Ur said.
"The urban settlement pattern was replaced by a much more rural pattern where you have smaller towns," he said. "As a result you didn't get large concentrations of people at key points, which produced these large roads."
Why did the civilizations collapse? Ur said there are two theories. The first favors some sort of natural catastrophe like a volcanic eruption or meteor strike.
"I personally don't think that's case," Ur said. "What is more likely is these agricultural system we see manifested by these roads were relying too much on the yield from these fields. When they had a couple of not-so-good seasons, the system collapsed."
Pournelle said it was more than just a few poor harvests, adding the situation likely paralleled the Dust Bowl phenomenon of the 1930s, where extended drought coupled with past farming practices created an untenable situation where the land could no longer support the population.
"The Syrian government has been trying to reintroduce more agriculture in the area through irrigation. It's possible because of several dams on Euphrates and also through deep wells and pump irrigation. Now there are new techniques for bringing water in area. However, the water supply is not infinite. The wells already are dropping," she said.