The Spiro Mounds leaders controlled the area of Antlers and the rest of the Kiamichi River valley, as well as a large portion of what is now southeastern Oklahoma and adjacent states. The Mississippian culture was based along the Mississippi River and its tributaries. Its largest center was at Cahokia, just to the east of the Mississippi in present-day Illinois. The peoples had an extensive trading network that spanned the continent from the Gulf Coast to the Great Lakes. Spiro Mounds culture was also part of the Southeast Ceremonial Complex, an important culture which extended into what is now known as the Southeastern United States.