Flows 981 miles through a significant industrial region of the central United States. Historically seen as the border between the northern and southern United States, the Ohio is formed in downtown Pittsburgh by the confluence of the Allegheny and Monongahela Rivers, flowing past Wheeling, Cincinnati, Louisville, and Evansville, forming borders of five states before emptying into the Mississippi at Cairo, Illinois. Other major tributaries of the Ohio include the Kanawha, Kentucky, Tennessee, Wabash, and Cumberland Rivers.