Mound Builders, in archeology, early native North Americans who built large mounds, primarily in valleys of the Mississippi and Ohio rivers and the Great Lakes region. The chief mound building peoples were the Adena, the Hopewell and the Mississippian. Mound Builders were active from approximately 5000 B.C. to 600 B.C. Their mounds served as burial places, fortresses, or as platforms for temples or official residences. The pottery, jewelry, weavings, and stone carvings found buried in the mounds show that their builders were skilled craftspeople, and confirm that they were ancestors of Native Americans. Built entirely by human labor, thousands of mounds remain, ranging in size from 1 to 100 acres (0.4 to 40 hectares). Their shapes vary from geometric patterns to those resembling animals.