Sinnissippi Site, Sinnissippi Park, Sterling, Illinois. U.S. National Register of Historic Places. The site contains several Hopewellian Indian Mounds built between 500 B.C.E. and 500 C.E.
<a href="//commons.wikimedia.org/wiki/User:IvoShandor" title="User:IvoShandor">IvoShandor</a>
CC BY 2.5
<span class="int-own-work" lang="en">Own work</span>