Researchers have long debated the reasons behind the rapid rise and swift disappearance of Cahokia, a sprawling, ancient city-state near the modern city of St. Louis. Now an analysis of sediment cores reveals that the city’s ups and downs correspond to the timing of Mississippi River megafloods, according to a recent study.

Archaeological data show that agricultural settlements first appeared in the area around A.D. 400. Around A.D. 1050 there was a veritable boom at Cahokia, which became a major political and cultural center with a population in the tens of thousands. But by 1350—a span of only three centuries—Cahokia was gone. (Discover Cahokia.)

To uncover clues to the city’s fate, a research team led by University of Wisconsin-Madison