As American expanded west of the Mississippi contact was made with many Native American tribes. One tribe known as the mound builders populated over one third of the United States. The size of the empire made a capital city seem unlikely so instead of a central city the capital was kind of divided into three regional centers located across the middle of the United States.
One of these regional centers known as Spiro was located in Oklahoma near the Arkansas River. There the river provided fertile ground, transportation, and an extremely reliable source of water. The fruits of the river made the mid-sized community a center for trade and commerce. The centers wealth was distributed among the natives making it a rich area by Mound Builder standards. The mid-sized community yielded some pretty impressive mounds but one in particular was a burial mound. Known as Craig Mound the series of three humps concealed more than two thousand bodies. All of which were buried with their valuables making it ver notorious among grave robbing thieves. .
The second regional center known as Cahokia was the largest of the three. At one time the community held one hundred and twenty mounds, and had an estimated population of 25000 people. It was so large it would cover modern day London with room to spare. With a community that size a wall was necessary to separate commoners from the wealthy. Constructed around the inner city the wall stood fifty feet high and stretched nearly two miles. Tree trunks were driven into the ground then plastered together to make a wall both sturdy and unscaleable. Many mounds were located in and outside of the wall. One mound, which particularly stands out, covers seventeen acres and is about ten stories tall. Know as Monks Mound the huge hill was used as a calendar or time keeping device. It was estimated to have taken one hundred and sixty eight years to construct.