The Mason-Dixon Line. The name itself conjures images of a divided nation, a boundary both geographical and ideological. But where is the Mason-Dixon Line exactly? More than just a line on a map, it represents a pivotal piece of American history, originally surveyed to settle a colonial border dispute, and later becoming a symbolic division between the North and South, particularly concerning slavery. Understanding its location and history is key to grasping a significant aspect of the United States’ past.
The Origins of the Mason-Dixon Line: Settling Colonial Disputes
The story of the Mason-Dixon Line begins with conflicting land grants issued to Maryland and Pennsylvania. According to their respective royal charters, both colonies laid claim to the land situated between the 39th and 40th parallels. Adding to the complexity, the “Three Lower Counties” that would eventually become Delaware, gravitated towards Pennsylvania’s sphere of influence.
In 1732, Charles Calvert, the 5th Baron Baltimore and proprietary governor of Maryland, attempted to resolve the issue by signing an agreement with William Penn’s sons. This agreement proposed a boundary line somewhere between the disputed parallels and also aimed to relinquish Maryland’s claim to Delaware. However, Lord Baltimore later contested the signed document, asserting it didn’t reflect their agreed-upon terms, and refused to implement it. This disagreement escalated into violent clashes in the mid-1730s, known as Cresap’s War, as settlers aligned with either Maryland or Pennsylvania clashed over land claims.
The conflict remained unresolved until 1760 when the British Crown intervened, compelling Frederick Calvert, the 6th Baron Baltimore, to accept the 1732 agreement. As part of this resolution, the Penn and Calvert families commissioned a team of English surveyors, Charles Mason and Jeremiah Dixon, to meticulously survey and establish the definitive boundaries. Their task was to demarcate the lines between the Province of Pennsylvania, the Province of Maryland, Delaware Colony, and parts of Virginia.
Surveying the Line: Geography and Markers
Mason and Dixon’s survey commenced south of Philadelphia, Pennsylvania. Their line extended eastward to the Delaware River and westward to the then-boundary of western Virginia. They also defined the boundary between Delaware and Pennsylvania, which is notably a circular arc, and the Delaware-Maryland boundary, which runs roughly north-south to bisect the Delmarva Peninsula.
The Maryland-Pennsylvania boundary, the most famous segment of the Mason-Dixon Line, is primarily an east-west line situated at an approximate mean latitude of 39° 43′ 20″ N (WGS 84 datum). Interestingly, this east-west line isn’t a perfect geometric line but a series of connected lines, varying between latitudes 39° 43′ 15″ N and 39° 43′ 23″ N. Surveyors might describe it as an approximate rhumb line, resembling a segment of a small circle on the Earth’s spherical surface. An observer on this line would notice it curving away from their line of sight due to the Earth’s curvature, an effect not seen on the Equator, which is a great circle.
Mason and Dixon also extended the boundary westward between Pennsylvania and colonial western Virginia, an addition not initially in their charter but later confirmed. This westward extension is relevant to the later formation of West Virginia during the Civil War.
To mark their progress, Mason and Dixon placed stones every mile and more significant “crownstones” every five miles. These stones were shipped from England. Maryland-side stones are marked with an “M,” while Delaware and Pennsylvania sides bear a “P.” Crownstones are more elaborate, featuring the coats-of-arms of the Penn and Calvert families. Many of these original stones are still visible today, some protected by iron cages on public lands, though others have been lost or buried over time.
Mason and Dixon also verified previous surveys defining Delaware’s southern boundary from the Atlantic Ocean to the “Middle Point” stone, along the Transpeninsular Line. From this point, they surveyed nearly directly north to reach the Pennsylvania border. While resurveys have been conducted over the centuries, they haven’t substantially altered Mason and Dixon’s original work. Although individual stones might be slightly off from the precise intended line, the line connecting the stones legally constitutes the boundary.
The point where Pennsylvania, Maryland, and Delaware meet, known as The Wedge, is marked by Boundary Monument #87, or “MDP Corner,” dating back to 1935. This marker is intentionally offset. According to Dave Doyle of the National Geodetic Survey, the Maryland-Pennsylvania Mason-Dixon Line is precisely at 39° 43′ 19.92216″ N, and Boundary Monument #87 is situated on this parallel at 075° 47′ 18.93851″ W. Visitors wishing to see this tripoint are advised to seek permission from landowners or utilize the path from the arc corner monument, bordered by parkland.
The Mason-Dixon Line and Slavery: A Symbolic Divide
While initially established to resolve a colonial boundary dispute, the Mason-Dixon Line gained a far greater significance after Pennsylvania abolished slavery in 1781. The western extension of the line, along with the Ohio River, became the dividing line between free states and slave states. Although Delaware itself remained a slave state, the Mason-Dixon Line increasingly symbolized the cultural and political differences between the North and South.
The term “Mason-Dixon Line” as a descriptor for the division between free and slave states gained prominence during the Missouri Compromise debates of 1820. This compromise further solidified the line’s symbolic meaning in the context of slavery and national division.
Modern Recognition and Legacy
The Mason-Dixon Line continues to hold historical significance and is recognized in modern times. In 1963, during the bicentennial of the line, President John F. Kennedy marked the completion of a section of Interstate 95 crossing the Maryland-Delaware border. This was tragically his last public appearance before his assassination in Dallas just eight days later. The Delaware Turnpike and the Maryland section of the highway were subsequently designated the John F. Kennedy Memorial Highway, further commemorating the Mason-Dixon Line’s place in American history.
Today, where the Mason-Dixon Line is remains a question with both a geographical and historical answer. It is a physical line on the map, meticulously surveyed and marked by stones, defining borders between states. But it is also a powerful symbol of a nation divided and later reunited, forever etched in the American consciousness as the line that once separated freedom and slavery.
