The banks of the Mississippi in the Midwest aren't necessarily known for world-class cities (sorry, St. Louis). But between A.D. 1050 and A.D. 1200, a city flourished right across from what is today St. Louis that was larger than London in size. Cahokia was spread over six square miles (16 square km) and was home to as many as 20,000 people. Modern development covers much of the site, but archaeologists have discovered that Cahokians drank caffeinated beverages and played a game known as "Chunkey." The city may have included a wooden temple and a wooden Stonehenge-like structure, perhaps important for keeping track of solstices and equinoxes.