Emerald Mound- Mississippi

(pictures do not do this sight justice, but following the link below and reading more about it will help.)
Emerald Mound is the second largest
prehistoric ceremonial mound in the United
States. It has been preserved by the National
Park Service and stands near the Mississippi
section of the famed Natchez Trace Parkway.

Covering nearly eight acres, the mound was
used for a roughly 350 years by prehistoric
Native Americans who were the ancestors of
Natchez Indians. Its builders were people of
the Mississippian culture, a religious and
political movement that spread across the
Southeast and lower Midwest beginning in
around 900 A.D.
http://www.exploresouthernhistory.com/natchezemerald.html