During conquistador and explorer Hernando de Soto's early 16th century expedition in what would become the southeastern United States, he encountered Native American cities of great wealth. Cities equal to any other in the Americas. These were the cities of what archaeologists call the Mississippian culture. The cities were marked by the construction of large, truncated earthwork pyramid mounds, or platform mounds. Mounds still visible and preserved today in many places. This earthen work construction practice of America’s native populations was preceded by two earlier mound-building cultures: the Effigy tradition and the Hopewellian tradition.