The Mason-Dixon line is a historical boundary line in the United States that separated the free states from the slave states before the American Civil War. It was originally surveyed in 1767 by two English surveyors, Charles Mason and Jeremiah Dixon, to settle a boundary dispute between the British colonies of Maryland and Pennsylvania. Today, the Mason-Dixon line still serves as a cultural and geographic boundary between the Northern and Southern United States, and is often used to refer to the cultural differences between the two regions.