The land mass that was to become the city of New Orleans was formed around 2200 BC when the Mississippi River deposited silt creating the delta region. Before Europeans founded the settlement, the area was inhabited by Native Americans for about 1300 years. The Mississippian culture peoples built mounds and earthworks in the area. Later Native Americans created a portage between the headwaters of Bayou St. John (known to the natives as Bayouk Choupique) and the Mississippi River. The bayou flowed into Lake Pontchartrain. This became an important trade route. Archaeological evidence has shown settlement here dated back to at least 400 A.D.