Mason-Dixon Line

Lat/Long: 39.716667, -75.783333

English astronomers Charles Mason and Jeremiah Dixon established the Mason-Dixon Line between 1763 and 1767 in order to settle a boundary dispute that the Penn and Calvert families—the proprietors of Pennsylvania and Maryland, respectively—submitted to a British court in 1735. Mason and Dixon's Line came to be known simply as the Mason-Dixon Line. In 1820, the Missouri Compromise used the line to delineate the boundary between free and slave states. In the years leading up to the Civil War, the Mason-Dixon Line was generally used and understood to be the symbolic line dividing the North from the South—politically and socially as well as geographically. It forms most of the present-day southern boundary of Pennsylvania. The western portion of the line became the boundary between Pennsylvania and Virginia and, later, West Virginia (after the latter was admitted to the Union). The line also formed the northern boundaries of Virginia, then West Virginia, and constitutes the present-day northern boundary of Maryland as well as the westernmost boundary of Delaware.

Courtlandt Canby, The Encyclopedia of Historic Places (New York: Facts on File, 1984), 2:575; Michael Martin and Leonard Gelber, eds., The New Dictionary of American History (New York: Philosophical Library, 1952), 388.