The Adena and Hopewell built mounds as sites to bury their dead.
The Mississippians continued this tradition, but they also built a new type of mound, large pyramids with flat tops. The tops of the mounds were places where religious leaders lived and performed rituals. Some later mounds were made as fortifications to keep enemies out.
Mound-building itself may also have served a social role by helping people live peacefully with one another.
In trading centers such as Poverty Point, where people from many groups came together, working side by side on these great projects may have taught different peoples how to get along.