Who'd a Thunk It?

Jeepers, imagine a city of 20,000 people in our Midwest in the year 1050 or so . . . can you? It's mind-boggling. But there was such a place, and apparently it was quite the sophisticated metropolis with cited evidence of peoples from various locales around (what is now) the country having spent some time there. Of course not all the answers are provided; there will probably always be some questions. But it's sure interesting to learn of, read about, and ponder what brought about its creation . . . and its demise. Hmmm.