Came across this book this weekend:
Ancient monuments of the Mississippi Valley
https://archive.org/details/ancientmonuments00squi/page/n17
Published in 1848. Blew my mind. About so many different “mounds” (a.k.a. pyramids) from ancient builder.s Many with underground tunnels, sepulchres… w/in habitations where there were altars. Human sacrifice occurring was a substantial assumption by the authors. They referred the mounds as “truncated pyramids”.
Sun worshippers.
Lots in Ohio.
Never learned about this in US history growing up. Did you?