The prehistoric Indians archaeologists call the Mound Builders lived in the area that is now the Mississippi and Ohio River Valley areas of the United States from 800 B.C. to A.D. 500.
These people built some 6,000 burial mounds, forts, and other earthen structures, some of which survive today.
One of the most impressive is an effigy mound called Serpent Mound, near Peebles, Ohio, in Adams County near the Kentucky border.
This mound, which looks like an uncoiling snake, averages 3 feet (91 cm) high and is almost 1,320 feet (402 m) long.
Constructed about 2,000 years ago, it was evidently not a burial mound because no burial objects have ever been found in it.