Archaeologist Andrew Reinhard has dug through humanity’s past among ancient ruins in Greece. These days, though, he digs a little closer to home.

Beneath the freeways of East St. Louis in Illinois there lie the ruins of a city built nearly a millennium ago, around towering earthen pyramids. Today called Cahokia, it held as many as 40 thousand people, and their influence spread throughout the southeast U.S. — mostly due the popularity of a game called chunkey.