Who all explored the Mississippi.

There was a civilization there before we discovered it.

Explanation:

They were called the Mississippians. The Mississippian culture was the largest and most complex society that lived in prehistoric Tennessee. Mississippian people lived in and around the state from about 1,000 A.D. to 1,500 A.D. This group is also referred to as the mound builders, because they built many large ceremonial mounds within fortified towns.

i believe it was spain