Surveying the Mason Dixon Line

The Mason-Dixon line, although drawn in 1763, is still used today to describe the division between the northern and southern parts of the United States.

The area was first surveyed by Charles Mason and Jeremiah Dixon to settle a property dispute. Although the line would come to have historical importance years later, it was first drawn to settle a dispute between descendants of George Calvert of Maryland and William Penn of Pennsylvania over the boundary between the two states. According to the charters originally granted to Calvert and Penn for establishing Maryland and Pennsylvania, respectively, the land between the 39th and 40th parallels belonged to both Maryland and Pennsylvania. As a result, the two sides argued over the boundary for several decades. The biggest problem with this that under Maryland’s claim, Philadelphia would actually be within Maryland, not Pennsylvania, and both sides wanted to lay claim to the town.

The compromise was finally drawn from 1763 to 1765 by Charles Mason and Jeremiah Dixon, an astronomer and a surveyor, both from England. The compromise set the boundary between southern Pennsylvania and northern Maryland at 15 miles south of Philadelphia, granting Philadelphia to Pennsylvania. First, they precisely pinpointed the area fifteen miles south of Philadelphia, erecting a limestone benchmark at this point. Then, they began surveying west of this point, which was rugged land with many Native Americans living in the region. Although they set out to survey 233 miles of land, but these hazards kept them from completing this goal. In 1767, the Mason-Dixon line had been almost completely surveyed by the pair, finally settling the dispute. The line as originally surveyed by the pair was marked by stones every mile and larger “crownstones” every five miles. Though many today are missing or buried, some are still visible.

Over five decades later, the area would again be thrown into controversy, although this time on a national scale. The same boundary delineated by the Mason-Dixon line became the main debate of the Missouri Compromise of 1820. This compromise used that line as the boundary between southern (slave) states and northern (free) states, as Pennsylvania had officially abolished slavery in 1781, while Maryland was still a slave state. According to the compromise, the states above the line would be free states, while those below the line could be slave states. The line surveyed by Mason and Dixon was extended west to the Mississippi River at this time. It also forms parts of the boundaries of Delaware and West Virginia.

In history, the name “Mason-Dixon line” symbolizes much more than a compromise between two states on boundaries; it has become associated with the struggle between slave and free states which would eventually be resolved only by the Civil War. Although the term Mason-Dixon line originally referred to the boundary dispute compromise, by the mid-nineteenth century it came to symbolize to divide between slavery and discrimination, in the south, and freedom, in the north. It can also be used to describe the indefinable cultural boundary between north and south.

Charles Lee Iner, RLS
May 2010 

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