I grew up around St. Louis and frequent visits to the Cahokia Mounds were a part of my upbringing. I still visit every year or so. It used to be just a place to go for picnics, with a small museum, but in the past few years they have gone to great lengths to preserve the area as a historical/archaelogical site, and the new museum is very informative. It's a worthwhile stop for anyone passing through the area.
I've been there twice. Most recently two years ago. I was under the impression that they were unsure of why the society declined and disappeared. I was more under the impression that it may have been do to climatic factors.
Why does the United Nations Flag fly at this site?
I've only been to Cahokia once. Fascinating site. What stuck me was the reconstructed wall. A simple palisade would not have been a surprise, but the park shows (based, I presume, on posthole traces) a bastioned wall with towers and a simple but still obvious gate complex -- in short, a developed piece of military architecture. Do you know if there is any evidence of large scale warfare at the site?
That stretch of the Mississippi was also a notorius hangout for river pirates. (I'm not making that up.)
L