Mason–Dixon Line

In the USA, the boundary line between Maryland and Pennsylvania (latitude 39° 43' 26.3" N), named after Charles Mason (1730–1787) and Jeremiah Dixon (died 1777), English astronomers and surveyors who surveyed it 1763–67. It is popularly seen as dividing the North from the South.

The two colonies had argued for almost a century, and armed skirmishes over the boundary during the early 1730s erupted into Cresap's War )1736–38. In 1760, the two colonies agreed to allow Mason and Dixon to delineate the line. For the period leading up to the Civil War, the Mason-Dixon line marked the border between free and slave states.