section_path: North America/Lithic and Archaic periods/Middle Archaic period
section_name: Middle Archaic period
paragraph_text: Middle Archaic period
  
  After the migration or migrations, it was several thousand years before the first complex societies arose, the earliest emerging about seven to eight thousand years ago. As early as 5500 BCE, people in the Lower Mississippi Valley at Monte Sano and other sites in present-day Louisiana, Mississippi, and Florida were building complex earthwork mounds, probably for religious purposes. Beginning in the late twentieth century, archeologists have studied, analyzed, and dated these sites, realizing that the earliest complexes were built by hunter-gatherer societies, whose people occupied the sites on a seasonal basis. Watson Brake, a large complex of eleven platform mounds, was constructed beginning in 3400 BCE and added to over 500 years. This has changed earlier assumptions that complex construction arose only after societies had adopted agriculture, and become sedentary, with stratified hierarchy and usually ceramics. These ancient people had organized to build complex mound projects under a different social structure.