The Mound Builders were a TRIBE of Native Americans who lived in the Eastern and Midwestern United States from about 800 BCE to 1500 CE. They are known for their construction of earthen mounds, which were used for religious and ceremonial purposes. The mounds were also used as burial sites and for defensive purposes. The Mound Builders were skilled farmers and hunters, and they developed a complex trading network. They left behind a rich cultural legacy that is still studied today.