Aerial View

One of the things which strikes me the most about the Indian Mounds is that none of them are meant to be view beyond their initial construction.  Their very design makes them almost impossible to fully without viewing them from the air (something impossible for a people at the technological level of the mound building cultures) and after the initial effort of their construction, there would be nothing to draw attention to them as non-natural features.   They seem almost to have been designed to be hidden.  

The fact that their true shape would be most visible from the air reminds me of the Nazca Lines, which are similar in kind, if not in size.  The importance of these constructions seems to have been intensely personal, of significance only to the builders and their gods, not requiring any attention by outsiders to make them important.