Great empires come and go, but it's not clear why some of them fell. New clues to the demise of two dynasties may have just emerged from a cave.

Evidence found in a cave near Jerusalem reveal increasingly dry weather from 100 A.D. to 700 A.D., a period that coincided with the fall of both Roman and Byzantine rule in the region.

The researchers are quick to point out that they have not discovered a cause-and-effect relationship, however.

"Whether this is what weakened the Byzantines or not isn't known, but it is an interesting correlation," said University of Wisconsin-Madison professor John Valley, who led the research. "These things were certainly going on at the time that those historic changes occurred."

The findings will be detailed in an upcoming issue of the journal Quaternary Research.

The work involved geochemical analysis of a stalagmite from Soreq Cave in the Stalactite Cave Nature Reserve near Jerusalem. Rain flushed organic matter from the surface into the cave, and it was trapped in mineral deposits that formed layers on the stalagmite.

Geology graduate student Ian Orland determined annual rainfall levels for the years the stalagmite was growing, from approximately 200 B.C. to 1100 A.D.

Similar research has been done before to look at decades worth of rainfall. In fact the technique has been used to show that centuries-long droughts plagued in North America thousands of years ago.

But Orland used an advanced ion microprobe to give greater detail through more layers, revealing rainfall patterns within individual seasons.

Their detailed climate record shows that the Eastern Mediterranean became drier between 100 A.D. and 700 A.D., a time when Roman and Byzantine power in the region waned, including steep drops in precipitation around 100 A.D. and 400 A.D.

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