ST. LOUIS, MISSOURI—According to a statement released by Washington University in St. Louis, Caitlin Rankin, now of the University of Illinois at Urbana-Champaign, and her colleagues analyzed soils around an earthen mound dated to between A.D. 1050 and 1400 at Cahokia Mounds State Historic Site, which is located in southwestern Illinois. The ancient city, home to some 15,000 people around A.D. 1100, was surrounded by a wooden palisade made from tens of thousands of trees. It had been suggested that the city was abandoned because deforestation of the uplands surrounding Cahokia caused devastating environmental problems, including flooding in local creek drainages. But Rankin’s investigation of the Cahokia Creek floodplain revealed that the mound had been constructed on a stable ground surface. She said that while there is evidence of heavy wood use at Cahokia, and area forests might have been depleted as a result, she found no evidence of flooding. Researchers will now need to look for other reasons why Cahokia was abandoned, the team concluded. To read about a possible catalyst for Cahokia's rise, go to "Around the World: Illinois."