Archaeological research indicates the mounds of North America were built over a long period of time by very different types of societies, ranging from mobile hunter-gatherers to sedentary farmers. The prehistoric mounds had a wide variety of forms and fulfilled a range of functions. Many served as burial mounds, individual or collective funerary monuments. Others were temple mounds, platforms for religious structures. Burial mounds were especially common during the Middle Woodland period (c.100 B.C.-A.D. 400), while temple mounds predominated during the Mississippian period (after A.D. 1000).
The earliest mounds in the United States have been found at Watson Brake near Monroe, La.; they were built in the late 4th millennium B.C. The purpose of these 11 mounds is unclear. Other mounds date to the 3d millennium B.C. The Archaic mound-building tradition culminated at the Poverty Point Site, in West Carroll Parish, La., between 1800 B.C. and 500 B.C. Six concentric ridges surround two large mounds, one of which reaches 65 ft (20 m) high.
During the Woodland period (c.500 B.C.-A.D. 1000), hunting and gathering was combined with a set of domesticated native agricultural plants (sunflower, goosefoot, erect knot weed, and may grass) to bring about increased population densities and a greater degree of sedentism throughout the Ohio and Mississippi valleys. The Middle Woodland period (c.200 B.C.-A.D. 400) saw the construction of elaborate earthworks from the Great Lakes to the Gulf Coast. Large, mainly dome-shaped mounds appeared throughout the Ohio and Tennessee river valleys, some in the form of animal effigies. In the Hopewell culture, centered in S Ohio and Illinois, earthen geometric enclosures defined areas ranging from 2.5 to 120 acres (1 to 50 hectares), and some mounds reached 65 ft (20 m) in height. Mica, ceramic, shell, pipestone, and other material were traded over a vast area, indicating the growth of a system of widely shared religious beliefs but not overall political unity. Analysis of mortuary remains suggests Middle and Late Woodland communities were characterized by a system of social rank: Particular kin groups are believed to have had high social prestige, differential access to rare commodities, and control over positions of political leadership. In the Late Woodland period (c.A.D. 400-1000), burial mounds decreased in frequency, and the elaborate burial goods of the Hopewell culture largely disappeared. However, there was probably no general decline in social complexity or population density at this time.
In the Mississippian period (after A.D. 1000), maize agriculture spread throughout the East. Populations expanded and became increasingly sedentary. At Cahokia Mounds (near East St. Louis, Ill.) the largest earthwork in North America was built, a temple mound measuring nearly 100 ft high (30 m) and 975 ft long (300 m). Many large ceremonial centers with temple mounds appeared throughout the South, especially in the Mississippi Valley. After 1200, a set of distinctive motifs spread throughout the Southeast, from Oklahoma to N Georgia, on a variety of media, including shell, ceramics, and pipestone. Also found in this region are elaborate ceremonial copper axes and gorgets and sheet copper plumes. This complex of distinct motifs is called the Southern Cult; it could reflect—along with the temple platforms—the existence of a regional religion shared by a large number of local cultures. Mississippian societies are thought to have been complex chiefdoms, the most hierarchical form of political organization to emerge in aboriginal North America.
See C. Thomas, Report on the Mound Explorations of the Bureau of Ethnology (1894, repr. 1985); R. Silverberg, Mound Builders of Ancient America (1968); W. Morgan, Prehistoric Architecture in the Eastern United States (1980); B. Fagan, Ancient North America (1991); G. R. Milner, The Moundbuilders (2004).