Literally, the Mason-Dixon Line (or "Mason and Dixon's Line") demarcated state boundaries between the Province of Pennsylvania, the Province of Maryland, Delaware Colony and parts of Virginia Colony in colonial North America and between their successor-state members of the United States.
Symbolically, the line became the boundary between the North and South, particularly with respect to slavery. Pennsylvania abolished slavery early while Delaware and Maryland remained slave states until the American Civil War.
Due to an incorrect map, the royal charter granted Maryland the territory north of the Potomac River up to the fortieth parallel, which would put Philadelphia, the major city in Pennsylvania, within Maryland. The Calvert family, which controlled Maryland, and the Penn family, which controlled Pennsylvania, engaged two British surveyors, astronomer Charles Mason and surveyor Jeremiah Dixon, to survey what became known as the Mason-Dixon line which would form the boundary between their two colonies. They ran this line for 244 miles (392 kilometres) between 1763 and 1767, until a group of Native Americans forced them to quit their progress westwards. This boundary between Pennsylvania and Maryland was resurveyed in 1849, then again in 1900.
Mason and Dixon's survey also fixed the boundary between Delaware and Pennsylvania and the approximately north-south portion of the boundary between Delaware and Maryland. Most of the Delaware-Pennsylvania boundary is an arc, and the Delaware-Maryland boundary does not run truly north-south because it was intended to bisect the Delmarva Peninsula rather than follow a meridian. However, the Maryland-Pennsylvania boundary is a true east-west line. The line also traced the border between Pennsylvania and West Virginia (originally part of Virginia).