Why were mounds built?

Question

explain why Adena Hopewells and the Mississippi and built a mound 

Answer 1

You'll have to refer to your course materials.  The Caddo people around East Texas built mounds and lived on them, and buried their high-ranked people in them.

 

I'm not precisely sure whether the mounds also had a defensive (castle-like) purpose, or whether there was occasional flooding that the mound kept them up off of, or what.