The lack of discernible defenses at other sites suggests peaceful periods. The purposes of some of the most ancient mounds are still shrouded in mystery. Some societies buried their dead in mounds with great solemnity and ceremony. Other cultures built temples atop the mounds and worshippers approach by climbing steep stairs or ramps. Still other earthworks were symbolic for power for the leaders who dwelled atop them.
Many mounds show a profile of successive layers, built gradually over many years of occupation.
Ga. Archeologists debate how and why the Mississippian moundbuilding cultures declined dramatically in the 1500s. Some experts think they may have been too successful. Large numbers of people competing for resources created tension, as did the class structure. Sanitation in the crowded river towns could have triggering an outbreak of epidemics. Another hypothesis states that the ending date of the Mississippian culture was 1540-50, after the passing of the Soto expedition through the Southeast.