Mound Builders, in archaeology, is a general term used to refer to the peoples who constructed earthen mounds and other earthworks in eastern and central North America during prehistoric times. Far from being the product of a single, uniform culture, the mounds and earthworks were built at various times from about 1000 BC to after AD 1500 by many different Indian societies. This activity was concentrated in a large area extending from the Appalachian Mountains west to the eastern edge of the prairies and from the Great Lakes area to the Gulf of Mexico.

Archaeological work has documented prehistoric mounds and earthworks numbering in the tens of thousands. The total number constructed will never be known, however, because a great many have been destroyed by natural forces such as floods, by farming, and by other human activities.

The earthen constructions have been classified into three principal categories: burial mounds; platform or temple mounds, on which important public and private buildings were placed; and circular and geometric ceremonial earthworks. Each of these general groups can be divided into smaller units representing temporal and cultural differences that have been identified throughout the large area in which the mounds and earthworks are distributed. Archaeologists recognize two major traditions of the mound-building cultures--the Woodland and the Mississippian.

Woodland cultural complexes are known to have developed in eastern North America from about 1000 BC to the early historic period (AD ca1700). The mounds associated with the Woodland tradition are primarily burial mounds, although circular and geometric earthworks also appeared in some areas.

One of the best-known Early Woodland complexes is referred to as the Adena culture. This mound-building cultural complex was located in the central Ohio Valley of present-day southern Ohio and contiguous areas of southeastern Indiana and northern Kentucky, and in the lower Kanawha Valley of West Virginia to as far east as Pittsburgh, Pa. The Adena mounds were constructed from the first half of the 1st millennium BC to early in the 1st century AD. The early mounds are relatively small and simply built and generally enclose only a few burials. Many of the late Adena mounds were much larger (from 20 to 80 ft high), were apparently constructed over many years, and contained numerous burials, some of them in log tombs. The Adena people also constructed earthen circles enclosing an interior ditch with an entryway. Some of the larger examples, such as Braddock Mound, near Fredericktown, Ohio, had a burial mound in the center of the circle. Other Early Woodland groups from the Great Lakes to the Gulf also erected burial mounds, but theirs were not as numerous or as complex as those of the Adena culture.

The late 1st century BC to about AD 400 marks the major period of burial-mound construction from southern Florida to northeast Texas and from New York to Minnesota. Most of the Middle Woodland societies in eastern North America were connected through trade, exchange, and common cultural patterns with the Hopewellian societies, which represent the most highly developed culture of the period, centered in southern Ohio and the Illinois Valley. The largest and most elaborate mounds, built in southern Ohio, were often associated with complex geometric earthworks in the form of circles, rectangles, octagons, parallel walls, hilltop fort-like constructions, and other forms. The precise function of these earthworks is unknown. The largest and best preserved, at Newark, Ohio, covered about 2 sq. mi. None of the other Middle Woodland societies produced such complex constructions as those of the Hopewellians, who are also noted for their fine stone sculptures, tools, pottery and figurative ornaments cut out of copper or mica.

Late Woodland societies in the upper Mississippi valley of Illinois, Iowa, Wisconsin and Minnesota erected effigy mounds in the period from about 400 to 1100. These burial mounds were sculpted in the form of bird, animal and human representations, such as the Marching Bears Mound in Wisconsin or in dome-shaped, curvilinear patterns. In many of these mounds, the burials were apparently placed in the area corresponding to the heart of the effigy figures, which were often more than 325 ft. long but generally only about 3 to 6 ft. high.

Elsewhere during the Late Woodland period (400-700) mounds of simple construction continued to be erected throughout a wide area in the East. New burial techniques at mound sites in the Ohio, Indiana, Kentucky, Illinois and Missouri area included the use of stone vaults and cists to enclose human remains.

Although gourds, squash and a variety of seed plants were cultivated by Woodland Indian societies, a major dependence on maize cultivation did not develop in eastern North America until after AD 700; beans became another predominant crop grown by sedentary eastern peoples by about the year 1000. The large-scale farming of these plants was a major factor in the development of a new cultural tradition--the Mississippian--and the increased size of Mississippian settlement populations.

Beginning about 700 in the flood plains of the central and lower Mississippi and its tributaries, many towns and villages developed, characterized by the erection of palisades and flat-topped, rectangular mounds that served as bases for temples and other important structures. The fortified settlements ranged in size from a few platform mounds and an estimated population of about 200 people to large political and religious centers, such as the Cahokia Mounds, across the Mississippi from present-day Saint Louis, Mo. containing 10 to 50 or more platform mounds and with populations of 500 to perhaps 10,000 people.

Although most Mississippian groups buried their dead in cemeteries, the construction of the Woodland type burial mounds did not disappear entirely. At the larger centers the elite families were sometimes placed in special burial mounds with elaborate grave goods representing their status in the society. These burials took place from about 1000 to 1500, when Mississippian culture was at its peak; the imposing monuments and associated artifacts--including outstanding pottery, weavings and stone carvings are a reflection of the most advanced prehistoric Indian groups in eastern North America.

The powerful chiefdoms of the Mississippian tradition were still flourishing when early European explorers such as Hernando de Soto visited southeastern North America in the 16th century. By the mid-17th century, however, mound building had ceased, and the populations of these groups had vastly declined, in part the result of internal warfare and the introduction of epidemic diseases through European contact.