section_path: North America/Lithic and Archaic periods/Late Archaic period
section_name: Late Archaic period
paragraph_text: Late Archaic period
  
  Until the accurate dating of Watson Brake and similar sites, the oldest mound complex was thought to be Poverty Point, also located in the Lower Mississippi Valley. Built about 1500 BCE, it is the centerpiece of a culture extending over 100 sites on both sides of the Mississippi. The Poverty Point site has earthworks in the form of six concentric half-circles, divided by radial aisles, together with some mounds. The entire complex is nearly a mile across.
  
  Mound building was continued by succeeding cultures, who built numerous sites in the middle Mississippi and Ohio River valleys as well, adding effigy mounds, conical and ridge mounds, and other shapes.