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No visible trace. But satellite data revealed the remains of an ancient settlement here.

Egyptians Went With the Flow

SAN FRANCISCO--Climate has long been a suspect in the collapse of the Old Kingdom of ancient Egypt. Using satellite images of ancient settlements in the Nile delta, archaeologist Sarah Parcak has found new evidence for a hard-hitting drought.

Egypt's Old Kingdom flourished for more than 5 centuries. But this centralized, pyramid-building civilization collapsed around 2181 B.C.E., ushering in more than a century of civil war. Although Egyptologists believe political and economic issues helped topple the Old Kingdom's central government, tomb inscriptions and climate records from soils and cave formations suggest that long-lasting drought may have shrunk the Nile's flow and contributed to the instability.

Searching for evidence of drought, Parcak, an archaeologist at Cambridge University, examined satellite images of the northeast delta, a region of low-lying land laced with small branches of the many-fingered Nile. In the satellite images, modern-day towns are hard to distinguish from the mounds of ancient decomposing mud-brick houses, known as tells. The tell-tale clue is that these silty ruins retain more water than modern towns. When Parcak manipulated the satellite images to highlight regions with more water in the soil, even tells partially covered by modern towns stood out sharply. The technique located 95% of the known tells in the region and uncovered 50 previously unknown sites, Parcak reported here 9 December at a meeting of the American Geophysical Union.

Parcak estimated the dates of the new sites from pot sherds. Combining those dates with dates from the known sites, she estimated the abundance of towns in each of the periods of Egyptian history. Twenty-seven towns were dated to the time of the Old Kingdom, but only four were inhabited during the chaotic period after it. Because variations in the Nile's flow affect the location and size of the delta waterways, Parcak argues that these towns, each positioned to take advantage of the irrigational and navigational potentials of the rivers, would have been left high and dry, then abandoned as the Nile's flow diminished.

The explanation seems reasonable, says Stephen Harvey, an Egyptologist at the University of Chicago's Oriental Institute, but he cautions that linking human behavior to climate trends is tricky business. Even so, Parcak's technique looks very promising. "Recognizing 50 new tells in the northeast delta is tremendous," he says. "Whether or not climate caused the change, the satellite images let us talk in all sorts of new ways about variability in the region over time."

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