The Mason-Dixon Line History

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Mason-Dixon Line History Homepage

Mason–Dixon Line

Mason-Dixon Line History
Mason-Dixon Line History.jpg
Mason-Dixon Line Marker


Rebel, Yankee, Northerner, Southerner, and American culture all come to mind when we hear someone discuss the famous Mason-Dixon Line. What exactly is the Mason and Dixon Line and why was it created in the first place. Does the Mason-Dixon Line really separate the North and South? These are just some of the questions that are discussed on the Mason-Dixon Line History page, which also includes answers to many of the common questions about the Line. This lesson will allow the student to know where the Mason-Dixon Line is located, what states are included in the Mason-Dixon Line, why it is called and named the Mason-Dixon Line, as well as some of the political and cultural differences between Northern and Southern states of the historic Line. While a simple yet crude Mason-Dixon Line map shows the basic geography, the current states and their relationship to the Line, other maps have been enlarged to give the Mason and Dixon Line its significance to the nation as a whole. Lastly, have borders of the Line changed, if so why and how.

The Mason–Dixon Line, or Mason and Dixon's Line, is a demarcation line between four U.S. states, forming part of the borders of Pennsylvania, Maryland, Delaware, and West Virginia (then part of Virginia). It was surveyed between 1763 and 1767 by Charles Mason and Jeremiah Dixon in the resolution of a border dispute between British colonies in Colonial America. Since the first official usage of the term "Mason and Dixon Line" during congressional debates over the Missouri Compromise of 1820, popular speech continues to reference the Mason-Dixon Line symbolically as a cultural, political, and social boundary, or dividing line between the Northern and Southern United States. From Mason-Dixon comes the term "Dixie," a name applied to states south of the line, which historically are the Southern states. Politically, the Mason-Dixon Line has long since served as the dividing line between the red and blue states, meaning the dominant line separating the nation's Republicans and Democrats. Leading up to the American Civil War, the Mason-Dixon Line was the nation's sectional boundary separating Northern and Southern states, or the North and South, by sectionalism. During the American Civil War (1861-1865), citizens residing in states north of the line were referred to as Yankees while persons south of the line were called Rebels. Immediately following the war, the Mason and Dixon Line was quoted as a cultural, social, and political boundary. Presently, while the Mason-Dixon Line, or Mason-Dixon, remains the nation's expository boundary separating the North and South, it represents the bisection of continuing sectional differences in political and social ideologies.

The original Mason-Dixon Line
Mason-Dixon Line.gif
Original Mason-Dixon Line Map

The "Mason and Dixon Line," commonly known as the "Mason-Dixon Line," was originally the boundary between Pennsylvania and Maryland.
In the 1800s the Mason-Dixon Line became symbolic of the nation's division between the "free states" and "slave states" from the Missouri Compromise of 1820 until the end of the American Civil War in 1865. Although Pennsylvania abolished slavery before the end of the American Revolution, Maryland, Delaware, Kentucky, and Missouri, also known as Border States, remained slave states until the end of the war.
Historically, the Mason-Dixon Line served to settle a border dispute between the Penn and Calvert families, but today the boundary simply illustrates sectional differences between North and South, Northerner and Southerner, as the diverging social, cultural, and political .  
First Usage
The first usage of the term "Mason and Dixon Line" was the political coinage of "Mason-Dixon Line" in the congressional debates over the bill known as the Missouri Compromise of 1820, which sought to define the northern limit of the slave-owning states.

Mason-Dixon Line Map, aka Mason and Dixon Line Map
Mason-Dixon Line Map.jpg
Mason-Dixon Line Map. Enhanced to Scale Map. Mason-Dixon Line History Lesson.

From 1763 to 1767, Charles Mason and Jeremiah Dixon surveyed and marked most of the boundaries between Maryland, Pennsylvania and the Three Lower Counties that became Delaware. The survey, which would be known as the Mason and Dixon Line, or Mason-Dixon Line, was commissioned by the Penn family of Pennsylvania and Calvert family of Maryland to settle their long-running boundary dispute.
After the Civil War, the line continued to be considered a cultural boundary. Some have viewed the Mason-Dixon Line continuing westward from Pennsylvania down the Ohio River to the Mississippi River, and crossing the Mississippi to place Arkansas, Louisiana and Texas south of the line. Debate whether Border States such as Missouri, Kentucky, Maryland and West Virginia belong on the north or south side of this boundary line continues to this day. A common assumption of the split between Northern and Southern U.S. lies between Virginia and West Virginia, however. Maryland and Pennsylvania both claimed the land between the 39th and 40th parallels according to the charters granted to each colony. The 'Three Lower Counties' (Delaware) along Delaware Bay moved into the Penn sphere of settlement, and later became the Delaware Colony, a satellite of Pennsylvania.
In 1732 the proprietary governor of Maryland, Charles Calvert, 5th Baron Baltimore, signed an agreement with William Penn's sons which drew a line somewhere in between, and also renounced the Calvert claim to Delaware. But later, Lord Baltimore claimed that the document he signed did not contain the terms he had agreed to, and refused to put the agreement into effect. Beginning in the mid-1730s, violence erupted between settlers claiming various loyalties to Maryland and Pennsylvania. The border conflict between Pennsylvania and Maryland would be known as Cresap's War. The issue was unresolved until the Crown intervened in 1760, ordering Frederick Calvert, 6th Baron Baltimore to accept the 1732 agreement. As part of the settlement, the Penns and Calverts commissioned the English team of Charles Mason and Jeremiah Dixon to survey the newly established boundaries between the Province of Pennsylvania, the Province of Maryland, Delaware Colony and parts of Colony and Old Dominion of Virginia.

Mason-Dixon Line History
Mason Dixon Line Map Survey History.jpg
Mason-Dixon Line Historical Marker

The issue was unresolved until the Crown intervened in 1760, ordering Frederick Calvert, 6th Baron Baltimore to accept the 1732 agreement. As part of the settlement, the Penns and Calverts commissioned the English team of Charles Mason and Jeremiah Dixon to survey the newly established boundaries between the Province of Pennsylvania, the Province of Maryland, Delaware Colony and parts of Colony and Old Dominion of Virginia. After Pennsylvania abolished slavery in 1781, the western part of this line and the Ohio River became a border between free and slave states, although Delaware remained a slave state.

Mason and Dixon's actual survey line began to the south of Philadelphia, Pennsylvania, and extended from a benchmark east to the Delaware River and west to what was then the boundary with western Virginia. The surveyors 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 a circular 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.
The Maryland–Pennsylvania boundary is an east-west line with approximate mean latitude of 39 43' 20" N (Datum WGS 84). In reality, the east-west Mason-Dixon Line is not a true line in the geometric sense, but is instead a series of many adjoining lines, following a path between latitude 39 43' 15" N and 39 43' 23" N; a surveyor or mapper might call it an approximate rhumb line. As such, the line approximates a segment of a small circle upon the surface of the (also approximately) spherical Earth. An observer standing on such a line and viewing its path toward an unobstructed horizon, would perceive it to bend away from his line of sight, an effect of the inequality between the amount of curvature to his left and right. Among parallels of latitude, only the Equator is a great circle and would not exhibit this effect.

The surveyors also extended the boundary line to run or extend between Pennsylvania and colonial western Virginia, which became West Virginia after the American Civil War, though this was contrary to their original charter; this extension of the line was only confirmed later. The Mason–Dixon Line was marked by stones every mile and ”crownstones” every five miles, using stone shipped from England. The Maryland side says (M) and the Delaware and Pennsylvania sides say (P). Crownstones include the two coats-of-arms. Today, while a number of the original stones are missing or buried, many are still visible, resting on public land and protected by iron cages. Mason and Dixon confirmed earlier survey work which delineated Delaware's southern boundary from the Atlantic Ocean to the ”Middle Point” stone (along what is today known as the Transpeninsular Line). They proceeded nearly due north from this to the Pennsylvania border.

US Census Bureau Mason-Dixon Line Map of Boundary
US Census Bureau Mason-Dixon Line Map.jpg
Mason-Dixon Line Map. US Census Bureau Map of Boundaries.

Later the line was marked in places by additional benchmarks and survey markers. The lines have been resurveyed several times over the centuries without substantive changes to Mason and Dixon's work. The stones may be a few to a few hundred feet east or west of the point Mason and Dixon originally specified; in any event, the line drawn from stone to stone forms the legal boundary. According to Dave Doyle at the National Geodetic Survey, part of the National Oceanic and Atmospheric Administration, the common corner of Pennsylvania, Maryland, and Delaware, at The Wedge is marked by Boundary Monument #87. The marker ”MDP Corner” dates from 1935 and is offset on purpose.

Doyle said the Maryland–Pennsylvania Mason–Dixon Line is exactly:
39 43′ 19.92216″ N
and Boundary Monument #87 is on that parallel, at:
075 47′ 18.93851″ W.

The line was established to end a boundary dispute between the British colonies of Maryland and Pennsylvania/Delaware. Due to incorrect maps and confusing legal descriptions, the royal charters of the three colonies overlapped. Maryland was granted the territory north of the Potomac River/Watkins Point up to the fortieth parallel; Pennsylvania was granted land extending northward from a point "12 miles north of New Castle Towne," which is located below the fortieth parallel. The most serious problem was that the Maryland claim would put Philadelphia, which became the major city in Pennsylvania, within Maryland. A protracted legal dispute between the Calvert family, which controlled Maryland, and the Penn family, which controlled Pennsylvania and the "Three Lower Counties" (Delaware), was ended by the 1750 ruling that the boundary should be fixed as follows:

  Between Pennsylvania and Maryland: 

  The parallel (latitude line) fifteen miles south of the southernmost point in Philadelphia, measured to be at about 39 43' N and agreed upon as the Maryland–Pennsylvania line.
  Between Delaware and Maryland:
  The existing east-west Transpeninsular Line from the Atlantic Ocean to its mid-point to the Chesapeake Bay.
  A Twelve Mile (radius) Circle around the city of New Castle, Delaware.
  A "Tangent Line" connecting the mid-point of the Transpeninsular Line to the western side of the Twelve-Mile Circle.
  A "North Line" along the meridian (line of longitude) from the tangent point to the Maryland Pennsylvania border.
  Should any land within the Twelve-Mile Circle fall west of the North Line, it would remain part of Delaware. (This was indeed the case, and this border is the "Arc Line.")

The disputants engaged an expert British team, astronomer Charles Mason and surveyor Jeremiah Dixon, to survey what became known as the Mason–Dixon Line.

Mason-Dixon Location Marker
Mason-Dixon Marker.jpg
Mason-Dixon Marker

The Mason–Dixon line is comprised of four segments corresponding to the terms of the settlement: Tangent Line, North Line, Arc Line, and 39 43' N parallel. The most difficult task was fixing the Tangent Line, as they had to confirm the accuracy of the Transpeninsular Line mid-point and the Twelve-Mile Circle, determine the tangent point along the circle, then actually survey and monument the border. They then surveyed the North and Arc Lines. They performed this work between 1763 and 1767, and this actually left a small wedge of land in dispute between Delaware and Pennsylvania until 1921.

In April 1765, Mason and Dixon began their survey of the more famous Maryland-Pennsylvania line. They were commissioned to run it for a distance of five degrees of longitude west from the Delaware River, fixing the western boundary of Pennsylvania (see the entry for Yohogania County). However, in October 1767 at Dunkard Creek near Mount Morris, Pennsylvania, nearly 244 miles (392 km) west of the Delaware, a group of Native Americans forced them to quit their progress. In 1784, surveyors David Rittenhouse and Andrew Ellicott and their crew completed the survey of the Mason-Dixon Line to the southwest corner of Pennsylvania, five degrees from the Delaware River. Other surveyors continued west to the Ohio River. The section of the line between the southwestern corner of Pennsylvania and the river is the county line between Marshall and Wetzel counties, West Virginia. The boundary between Pennsylvania and Maryland was resurveyed in 1849, then again in 1900.

The Missouri Compromise of 1820 created the political conditions which made the Mason-Dixon Line important to the history of slavery. It was during the Congressional debates leading up to the compromise that the term "Mason-Dixon line" was first used to designate the entire boundary between free states and slave states.

On November 14, 1963, during the bicentennial of the Mason–Dixon Line, U.S. President John F. Kennedy opened a newly completed section of Interstate 95 where it crossed the Maryland-Delaware border. It was his last public appearance; 8 days later in Dallas, Texas, he was assassinated. The Delaware Turnpike and the Maryland portion of the new road were each later designated as the John F. Kennedy Memorial Highway.

Original Mason-Dixon Line Map
Mason-Dixon Line Map.jpg
Mason-Dixon Line Map, aka Mason and Dixon Line. US History.

(Sources and related reading below.)

Recommended Reading: A House Divided: Sectionalism and Civil War, 1848-1865 (The American Moment). Reviews: "The best short treatment of the sectional conflict and Civil War available... Sewell convincingly demonstrates that the conflict was a revolutionary experience that fundamentally transformed the Republic and its people, and left a racial heritage that still confronts America today. The result is a poignant discussion of the central tragedy of American history and its legacy for the nation." -- William E. Gienapp, Georgia Historical Quarterly. "A provocative starting point for discussion, further study, and independent assessment." -- William H. Pease, History. "Sewell's style is fast moving and very readable... An excellent volume summarizing the stormy period prior to the war as well as a look at the military and home fronts." -- Civil War Book Exchange and Collector's Newsletter. Continued below…

"A well-written, traditional, and brief narrative of the period from the end of the Mexican War to the conclusion of the Civil War... Shows the value of traditional political history which is too often ignored in our rush to reconstruct the social texture of society." -- Thomas D. Morris, Civil War History. "Tailored for adoption in college courses. Students will find that the author has a keen eye for vivid quotations, giving his prose welcome immediacy." -- Daniel W. Crofts, Journal of Southern History.

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Recommended Reading: CAUSES OF THE CIVIL WAR: The Political, Cultural, Economic and Territorial Disputes Between the North and South. Description: While South Carolina's preemptive strike on Fort Sumter and Lincoln's subsequent call to arms started the Civil War, South Carolina's secession and Lincoln's military actions were simply the last in a chain of events stretching as far back as 1619. Increasing moral conflicts and political debates over slavery-exacerbated by the inequities inherent between an established agricultural society and a growing industrial one-led to a fierce sectionalism which manifested itself through cultural, economic, political and territorial disputes. Continued below...

This historical study reduces sectionalism to its most fundamental form, examining the underlying source of this antagonistic climate. From protective tariffs to the expansionist agenda, it illustrates the ways in which the foremost issues of the time influenced relations between the North and the South.

Recommended Reading: Manifest Destiny: American Expansion and the Empire of Right (Critical Issue Book). From Booklist: In this concise essay, Stephanson explores the religious antecedents to America's quest to control a continent and then an empire. He interprets the two competing definitions of destiny that sprang from the Puritans' millenarian view toward the wilderness they settled (and natives they expelled). Here was the God-given chance to redeem the Christian world, and that sense of a special world-historical role and opportunity has never deserted the American national self-regard. But would that role be realized in an exemplary fashion, with America a model for liberty, or through expansionist means to create what Jefferson called "the empire of liberty"? Continued below…

The antagonism bubbles in two periods Stephanson examines closely, the 1840s and 1890s. In those times, the journalists, intellectuals, and presidents he quotes wrestled with America's purpose in fighting each decade's war, which added territory and peoples that somehow had to be reconciled with the predestined future. …A sophisticated analysis of American exceptionalism for ruminators on the country's purpose in the world.


Recommended Reading: Seizing Destiny: The Relentless Expansion of American Territory. Publishers Weekly: In an admirable and important addition to his distinguished oeuvre, Pulitzer Prize–winner Kluger (Ashes to Ashes, a history of the tobacco wars) focuses on the darker side of America's rapid expansion westward. He begins with European settlement of the so-called New World, explaining that Britain's successful colonization depended not so much on conquest of or friendship with the Indians, but on encouraging emigration. Kluger then fruitfully situates the American Revolution as part of the story of expansion: the Founding Fathers based their bid for independence on assertions about the expanse of American virgin earth and after the war that very land became the new country's main economic resource. Continued below...

The heart of the book, not surprisingly, covers the 19th century, lingering in detail over such well-known episodes as the Louisiana Purchase and William Seward's acquisition of Alaska. The final chapter looks at expansion in the 20th century. Kluger provocatively suggests that, compared with western European powers, the United States engaged in relatively little global colonization, because the closing of the western frontier sated America's expansionist hunger. Each chapter of this long, absorbing book is rewarding as Kluger meets the high standard set by his earlier work. Includes 10 detailed maps.


Recommended Reading: The Impending Crisis, 1848-1861 (Paperback), by David M. Potter. Review: Professor Potter treats an incredibly complicated and misinterpreted time period with unparalleled objectivity and insight. Potter masterfully explains the climatic events that led to Southern secession – a greatly divided nation – and the Civil War: the social, political and ideological conflicts; culture; American expansionism, sectionalism and popular sovereignty; economic and tariff systems; and slavery. In other words, Potter places under the microscope the root causes and origins of the Civil War. He conveys the subjects in easy to understand language to edify the reader's understanding (it's not like reading some dry old history book). Delving beyond surface meanings and interpretations, this book analyzes not only the history, but the historiography of the time period as well. Continued below…

Professor Potter rejects the historian's tendency to review the period with all the benefits of hindsight. He simply traces the events, allowing the reader a step-by-step walk through time, the various views, and contemplates the interpretations of contemporaries and other historians. Potter then moves forward with his analysis. The Impending Crisis is the absolute gold-standard of historical writing… This simply is the book by which, not only other antebellum era books, but all history books should be judged.

Sources: Cope, Thomas D.  1949.  Degrees along the west line, the parallel between Maryland and Pennsylvania.  Proceedings of the American Philosophical Society 93 (May 1949); Cummings, Hubertis Maurice, 1962.  The Mason and Dixon line, story for a bicentenary, 1763-1963.  Commonwealth of Pennsylvania, Dept. of Internal Affairs, Harrisburg, PA.; Danson, Edwin, 2001  Drawing the line : How Mason and Dixon surveyed the most famous border in America.   John Wiley & Sons, New York; Ecenbarger, William, 2000.  Walkin' the line: a journey from past to present along the Mason-Dixon.  M. Evans, New York; Latrobe, John H. B.  1882.  The history of Mason and Dixon's line: contained in an address, delivered by John H. B. Latrobe of Maryland, before the Historical society of Pennsylvania, November 8, 1854.  G. Bower, Oakland, DE.; Mason, A.H. (ed.) Journal of Charles Mason [1728-1786] and Jeremiah Dixon [1733-1779].  1969.  Memoirs of the American Philosophical Society vol. 76).  American Philosophical Society, Philadelphia; Nathan, Roger E.  2000.  East of the Mason-Dixon Line: a history of the Delaware boundaries.  Delaware Heritage Press, Wilmington, DE.; Pynchon, Thomas.  1997.  Mason & Dixon.  Henry Holt, New York; Sobel, Dava.  1996.  Longitude: the true story of a lone genius who solved the greatest scientific problem of his time.  Walker & Co., New York; The Federal and State Constitutions Colonial Charters, and Other Organic Laws of the States, Territories, and Colonies Now or Heretofore Forming the United States of America, Compiled and Edited Under the Act of Congress of June 30, 1906 by Francis Newton Thorpe, Washington, DC : Government Printing Office, 1909.

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