To resolve a long-simmering, sometimes-violent dispute between the Maryland and Pennsylvania colonies (as well as Virginia and Delaware), surveyors Charles Mason and Jeremiah Dixon carefully plotted this border between 1763 and 1767. Markers such as this one in Harney, Carroll County, were placed along the line at five-mile intervals. As the national debate over slavery simmered for the next century, the line came to be regarded as the unofficial border between North and South.
Kenneth K. Lam, Baltimore Sun photo
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