silversand wrote:

...there is a MASSIVE prehistoric city being excavated, called the East St Louis Mounds; this site is, "...the largest prehistoric dig in North America. It’s one of the biggest contiguous sites of a Mississippian city ever excavated."

I think virtually all the mound sites in the US were once connected...

sleepy wrote:

.....

But after seeing many of them it occurs to me that there might be a more basic reason: To be able to take refuge from flooding rivers.

Water is important for drinking, cooking, irrigation, fishing, hunting, and transportation... when you have thousands of people you need to be close to a lot of water... big rivers.

But... there is always the risk of floods... the Mississiooi River Valley is too wide to to find high ground to survive until the flood waters recede. All of the reasons that I mentioned above might have played a part but... survival was probably the motivation to carry a million baskets of dirt to build one mound............

GoinThisAway wrote:

I knew there are some mounds in Tennessee but I didn't know how close by until I got a call at work from an archeologist looking for topographic mapping of the Mound Bottom area in Cheatham County. Had to do a search on the internet but once I knew where to look a large mound was quite obvious on the topo map. This mound was protected by the State in 1973. There are others in the area but they're on private land.

As far as mounds being a refuge from flood waters, it's possible but for this mound on the Harpeth River probably not very likely. Although the mound is in a floodplain there is a lot of natural high ground nearby.