The Great Mortuary or Craig Mound (also called "The Spiro Mound") Credit:Wikimedia Commons
Spiro Mounds according to Wikipedia:
Spiro Mounds is an important pre-Columbian Caddoan Mississippian culture archaeological site located in present-day eastern Oklahoma in the United States.
Spiro Mounds is located in Spiro, Oklahoma. The site is a prehistoric Native American archaeological site that is open to the public.
The prehistoric Spiro people had developed a religious and political system.
The video below from Discover Oklahoma provides an overview of the Spiro Mounds.