Earthworks created by prehistoric cultures are common in the Midwest. The indigenous Native Americans have built many earth mounds over the centuries. Work that required many laborers was possible because local societies developed hierarchical structures with the elites to command the construction. The most common are conical mounds built as burial places.
Effigy Mounds in the Upper Mississippi River Valley in Iowa are especially interesting for their many animal-shaped earthworks. The largest of them is the Great Bear Mound that is 42 meters/ 138 feet long. There are also many simpler rectangular mounds that were used for ceremonial purposes. Even today, many Native American Tribes consider all mounds as sacred places.
