Potomac

A river of the United States, formed by two branches, which rise in the Alleghany Mountains, and unite 20 miles southeast of Cumber land, Md., from which point the river flows in a generally southeasterly course, 400 miles, and falls into Chesapeake Bay, where it is 6 to 8 miles broad, 75 miles from the ocean. Line-of-battle ships ascend to Washington, 120 miles from its mouth. The Potomac forms the greater part of the boundary between Virginia and Maryland. During the civil war, both Federal and Confederate armies cro ed several times the fords of the Upper Potomac, and severe actions were fought upon its banks. The largest army of the Union was named after it.