With a population between 10,000 and 30,000 in its heyday (A.D. 1050-1200) and a sprawling assortment of homes, storage buildings, temples, cemeteries, mounds and other monuments in and around what is now St. Louis and East St. Louis, Illinois, the ancient Native American city known as Greater Cahokia was the first experiment in urban living in what is now known as the United States.