Less than 10 miles from the Gateway Arch soaring over the modern St. Louis skyline, another set of symbolic structures rises above the Mississippi River. A network of 70 ancient earthen pyramids, these manmade features constitute the remains of one of the greatest civilizations ever to exist in the Americas.
Known as Cahokia Mounds State Historic Site, this topographical marvel dates to 700 A.D. and sprawls across 2,200 acres of present-day Illinois. A UNESCO World Heritage Site designation denotes its status as one of the most significant archeological preserves on the globe.
Mound Builder society was complex. Structures are precisely aligned to the movements of the sun and other important celestial bodies. Mounds also take different forms, with platform shapes designed for religious and political ceremonies, while canonical mounds were used for burials (one mound in particular held 300 skeletons, presumed to be human sacrifices). Despite its vast size and thriving culture, Cahokia residents had vanished by the 1300s—though exactly what prompted their demise remains a mystery.