“Restless Progress in America”: Drawing the Mason-Dixon Line

“When I found I had crossed that line,” recalled Harriet Tubman, “I looked at my hands to see if I was the same person. There was such a glory over everything . . . I felt like I was in Heaven.”

Such was the power of the Mason-Dixon Line. Within 75 years of its completion to resolve an eight-decade-long dispute between two colonial proprietors, a boundary line drawn in the 1760s by two English scientists had become a symbol of the growing rift in the young nation. For millions living in Antebellum America, Pennsylvania’s southern boundary represented a political as well as a psychological demarcation between freedom and enslavement, between North and South.

Today, the Mason-Dixon Line has lost much of its historic significance. The closest connection for 21st-century Americans may be “Sailing to Philadelphia,” singer and guitarist Mark Knopfler’s 2000 ode to  “stargazer” Charlie Mason and “Geordie boy” Jeremiah Dixon, who are “Sailing to Philadelphia / To draw the line / A Mason-Dixon Line.” But during the 18th and 19th centuries, the creation and existence of the line was of profound importance.

New World Proprietors at Odds

Both Maryland and Pennsylvania owe their foundation in part to the search for religious tolerance. In June 1632 Britain’s King Charles I awarded Cecil Calvert (1605–75), Second Lord Baltimore and a devout Catholic, a charter for a proprietorship in North America. Granted land stretching from the southern bank of the Potomac River to a “point which lieth under the Fortieth degree of north latitude,” Calvert named his colony Maryland to honor the king’s French consort, Henrietta Maria. Calvert’s North American outpost quickly embraced tobacco as its primary cash crop. Their economic fortunes now bound to the English market, Maryland planters soon emulated their southern neighbors in Virginia by importing African slaves to work their fields beginning in 1642.

Like Calvert, the Quaker William Penn (1644–1718) envisioned a New World settlement characterized by religious freedom. In 1681 he convinced King Charles II to satisfy the crown’s debt of ₤16,000 to his father with one of history’s largest individual land grants. Pennsylvania — literally “Penn’s woods,” a name chosen by the king that the proprietor unsuccessfully sought to reject —stretched south from the 43rd parallel to a “Circle drawne at twelve miles distance from Newcastle . . . to the beginning of the fortieth degree” of latitude and as far west as 5 degrees longitude from the Delaware River.

Penn almost immediately recognized the need to establish a clear demarcation between his holdings and those of the Calvert family. In August 1681 he sent a cousin to the Patuxent River estate of Charles Calvert (1637–1715), Third Lord Baltimore, on an unsuccessful mission to settle the matter. The two proprietors next met face-to-face in Annapolis in December 1682 and again failed to reach an understanding. At issue was as much as 4,000 square miles of territory. That same year Penn further aggravated Calvert when he leased the “Lower Counties on the Delaware” from the Duke of York. Penn’s control of this territory, to which Calvert also had a claim, gave his Pennsylvania colony much needed access to the sea. (Initially governed as one colony, Pennsylvania and the Lower Counties established separate legislatures by 1704, but shared a colonial governor until the American Revolution.) In 1685, after further negotiations had failed, the Board of Trade and Plantations in London set the boundary between Pennsylvania and Maryland at 40 degrees latitude north, extended westward to the Indian lands.

In 1735 this map was used as an exhibit in the case of the Penns against Calvert to settle the Pennsylvania–Maryland boundary dispute. Library of Congress

The Conojocular War

Neither Penn nor Calvert liked the Board of Trade’s decision and the dispute remained unresolved for nearly 50 years. During that time both proprietors died, bequeathing the controversy to their heirs. The ongoing boundary dispute led to frequent and often violent confrontations on the frontier. The Conojocular War — the best known of these flare-ups — pitted the cantankerous Thomas Cresap (c.1702–c.1790) against his neighbors and local law enforcement. In 1729 Cresap bought land from Maryland officials along the southern bank of the Susquehanna River near present-day Wrightsville, York County. His neighbors considered themselves Pennsylvanians and in 1732 accused him of shooting their cattle and horses when they strayed onto his land and of burning the homes of friendly Indians. Maryland governor Samuel Ogle (c.1694–1752) sprang to Cresap’s defense, assuring him that “so long as he behaves himself well, he shall be protected from any Insults of the Pennsylvanians.”

When the Lancaster sheriff tried to arrest him in 1734 for selling land parcels already owned by Pennsylvanians, Cresap shot and killed a posse member. Once again Governor Ogle stepped in, characterizing Cresap as “a very sober and modest Person” and instructing him to “defend himself  in Case any unjust attack should be made upon him.” Governor Patrick Gordon (c.1644–1736), Ogle’s Pennsylvania counterpart, responded by characterizing Cresap as a “publick Disturber of the Peace of both Governments.” Things came to a head two years later, when the Lancaster sheriff and 24 men surrounded Cresap’s cabin to arrest him for his earlier murder of Knowles Daunt.

Vowing that “they would not depart . . . until they had [Cresap] dead or alive,” the Pennsylvanians — whom Cresap labeled “Quakeing Dogs & Rogues” — set fire to his cabin, arrested him, and marched him off to Philadelphia. There he sat in jail for eight months, until King George II, taking notice of these colonial contretemps, commanded that no more land grants be made along the Pennsylvania–Maryland frontier. Nor, continued the king, were “any Tumults, Riots, or other outrageous Disorders to be Committed on the Borders.”

In 1732, while Cresap was beginning his one-man war with his Pennsylvania neighbors, the Board of Trade reaffirmed the decree of 1685. An agreement among Charles Calvert (1699–1751), Fifth Lord Baltimore, and William Penn’s sons John, Thomas and Richard called for a formal survey and relocated the northern border of Maryland 15 miles south of Philadelphia. In agreeing to this change, Calvert unwittingly ceded all the land that William Penn had claimed in 1681. By 1735 the dispute had found its way to the English courts in what became known as the Great Chancery Suit. Thousands of pounds in legal fees and 15 years later, the court issued a partial decision: the circle establishing the southeastern corner of Pennsylvania’s boundary was to be measured on a 12-mile radius from a center point in New Castle, Delaware. The remaining work of defining the boundaries was left to seven-man commissions to be formed in each colony.

This page from Mason and Dixon’s journal notes their arrival in Philadelphia to start the survey on November 15, 1763. National Archives

Yet another decade passed, during which efforts to delineate the boundaries outlined by the English courts proved beyond the capabilities of colonial surveyors. Increasingly frustrated, the governors of Maryland and Pennsylvania finally appealed to the proprietors in England to hire experienced professionals. Thomas Penn (1702–75) and Cecil Calvert (1702–65), brother of the Fifth Lord Baltimore, consulted with the London scientific community about how to establish the boundary survey and began assembling the scientific instruments that would be needed for the survey. In early August 1763 Penn and Calvert hired “two persons who . . . are well-skilled in astronomy, mathematicks, and surveying to mark, run out, settle, fix, and determine all such parts of the circle, marks, lines and boundaries.” By September, reported Thomas Penn, “Mr. Mason and Mr. Dixon have taken their passages with Captain Falconar . . . and they have with them the fine Sector, two Transit Instruments, and two reflecting Telescopes.” Charles Mason (1728–86) and Jeremiah Dixon (1733–79) arrived in Philadelphia on November 15, 1763, to begin what Mason would characterize as “my restless progress in America.”

Mason and Dixon Get to Work

When selecting Mason and Dixon, Penn and Calvert relied heavily on the recommendations of members of the Royal Academy of Science as well as interviews with the two surveyors. Both men were well-known in the English scientific community. Born in the village of Oakridge Lynch in Gloucestershire, Mason was a first-rate mathematician who had become the assistant astronomer at the Greenwich Observatory in 1756. Five years later he led one of several expeditions sponsored by the Royal Society to observe the transit of Venus, an infrequent celestial phenomenon during which the planet Venus passes between the Earth and the Sun. As his assistant for the expedition, Mason selected Jeremiah Dixon, a self-taught astronomer from County Durham who was five years his junior.

Mason and Dixon’s contract charged them with establishing two boundary lines — the West Line providing an east-to-west border separating Pennsylvania from Maryland, and the north-to-south Mid Line separating Maryland from the three Lower Counties, which today constitute the state of Delaware. Each man would receive £600 plus expenses once the project was completed; the two colonial commissions were to reimburse operating costs as the survey progressed. Before they would provide the surveyors with scientific instruments vital to the project, the commissioners made Mason and Dixon swear an oath to “use their best skills and knowledge and show no partiality to either Penns or Calvert.” The two men were also to keep a daily journal documenting their progress.

In 1764, as Charles Mason and Jeremiah Dixon traveled across the land on their mission to draw a border between Pennsylvania and Maryland, they passed through West Bradford Township, Chester County, where botanist and stonemason Humphry Marshall (1722–1801) was helping to build Martin’s Tavern. In this 2013 oil-on-canvas painting titled Meeting at Martin’s Tavern, Chester County artist Adrian Martinez imagines the encounter, with the surveyors flanking Marshall—Dixon, left, and Mason, right—and a Native American guide standing among the local inhabitants. Throughout their survey, Mason and Dixon often consulted with knowledgeable residents about the landscape. Courtesy Adrian Martinez

Mason and Dixon were expected to resolve complex scientific challenges amid far-from-ideal conditions. The wilderness settings in which they would carry out the surveys had recently seen violent encounters between Indians and white settlers. A royal proclamation a month before their ship reached Philadelphia had drawn an arbitrary and unpopular line along the crest of the Appalachian Mountains, prohibiting whites from settling on lands to the west of the boundary. And in December, as Mason and Dixon were just getting oriented, a vigilante group known as the Paxton Boys revenged various Indian depredations by murdering 21 peaceful Conestoga Indians living in Lancaster and for a time threatened Philadelphia.

Actual survey work could not begin during the winter months, so Mason and Dixon established their headquarters at John Harland’s plantation at the forks of the Brandywine River. There they took a series of painstaking astronomical readings to determine the southernmost point in Philadelphia. Thomas Penn and Cecil Calvert had agreed in 1732 that the latitude defining the West Line was to lie 15 miles to the south of this point. Taking astronomical readings in mid-winter was arduous duty, carried out by observers lying on their backs inside a portable observatory in subfreezing temperatures. Using an instrument called a zenith sector, they tracked the movement of stars across the night sky. Using the data they gathered, as well as star charts created by the Royal Society, Mason and Dixon could then mathematically calculate the exact latitude from which they were taking their measurements. In April 1764 Mason and Dixon began their first assignment—to survey and mark the boundary between Maryland and the three Lower Counties. William Penn’s charter had set his colony’s southeastern boundary with the Lower Counties as an arc with a 12-mile radius centered in New Castle. Mason and Dixon were to survey that arc as well as a Tangent Line to extend south to a midpoint on the peninsula halfway between Cape Henlopen on the Atlantic Ocean and the Chesapeake Bay. Land west of the  Tangent Line belonged to Maryland; land to the east went to the Lower Counties.

A diagram from Mason and Dixon’s journal showing their work on drawing the Tangent Line between Maryland and the Lower Counties. National Archives

Surveying the arc called for a series of complex calculations that had stumped Mason and Dixon’s predecessors. But by June the surveying party was able to complete the arc, place a “Post marked West” that set the latitude of the West Line, and begin marking the north–south boundary on the peninsula. The survey team included 39 men, two wagons and eight horses. Working six days a week from 7 a.m. until sundown, a crew of axmen cut down trees to clear an 8-to-9-yard-wide vista for the surveyors. Mason and Dixon then took the telescope readings and distance measurements necessary to chart the boundary line.

Distances were measured with a 66-foot-long wrought iron Gunter’s chain. Heights and angles were measured with a transit, which combined a compass and a telescope with which to take vertical and horizontal measurements. Mason and Dixon then used trigonometry to calculate distance, height and angles over uneven terrain. They marked each mile of the boundary with a wooden post and double-checked their measurements by observing the positions of the stars and making calculations every 11½ miles. Advancing between 1 to 3 miles a day, the crew completed the 82-mile-long boundary line by November 26, 1764.

Before returning to the Harland plantation for the winter months, Mason and Dixon delivered a progress report to the commissioners, who instructed them to begin the survey of the West Line in 1765. In January, Mason, the more curious of the two surveyors, traveled west to Lancaster “to see the place where was perpetrated last Winter the Horrid and inhuman murder of 26 Indians, Men, Women, and Children, leaving none alive to tell.” On his return trip, he encountered Samuel Smith, the retired sheriff of Lancaster County, who shared the story of Cresap and the Conojocular War of 30 years earlier.

Mason and Dixon returned to the field in early April 1765 to begin surveying the West Line, traveling through what Mason described as “a desolate country uninhabited by anything but wild Indians, bears, and rattlesnakes.” By late October the crew of more than 40 men had surveyed 117 miles from the “Post marked West” and was in sight of the Allegheny Mountains. After double-checking their work as they returned east for the winter, Mason and Dixon dismissed their crew and met with the commissioners in York for three days in mid-November to report on their progress. In response to a new set of instructions, the two surveyors recruited workers to help place 50 boundary stones along the Tangent Line. Imported from England as ballast in cargo ships, the rectangular stones weighed between 300 and 600 pounds and measured from 3½ to 4½ feet tall. The more elaborate markers featured the Calvert and Penn family coats of arms facing Maryland and Pennsylvania respectively, while others were more simply marked with an “M” or a “P.” By January 1, 1766, the work was com-pleted and Mason and Dixon retired once again to the Harland plantation and nearby Philadelphia for the winter.

The Pennsylvania side of the line markers featured the Penn family coat of arms.
The State Museum of Pennsylvania/Photo by Don Giles

The Calvert coat of arms appeared on the Maryland side of the markers. The State Museum of Pennsylvania/Photo by Don Giles

When work resumed in April 1766, the survey team moved ahead rapidly and by June 14 had reached Savage Mountain in the Appalachians, as far west as they were authorized to go. Turning back, they once again checked their work, this time relying on astronomical readings. By September Mason and Dixon were back in the Philadelphia area, where they received instructions from the commissioners to extend the boundary eastward from the “Post marked West” until it intersected the Delaware River and to set more boundary stones. By November an additional 35 stones marked the Tangent Line, and stones stood at each mile post for 65 miles along the West Line.

After much discussion at a year-end meeting, the commissioners decided to extend the survey past the 1763 Proclamation Line into Indian Territory, but only if the tribes of the Six Nations of the Iroquois would ensure safe passage for the survey party. Gen. Sir William Johnson, His Majesty’s Agent for Indian Affairs and someone who enjoyed close relationships with the tribes, was asked to negotiate an agreement. Mason and Dixon finally received permission to extend the survey to the Allegheny divide, 80 miles past the proclamation line, on June 3, 1767. A deputation of 11 Mohawks and three Onondagas would accompany the surveyors to monitor their activities.

The final stage of Mason and Dixon’s survey began on July 16, 1767. By September 26 the party had reached the banks of the Monongahela River. Although their contacts with Indians had been peaceful thus far, fear that Delaware and Shawnee war parties were in the area led 26 workers to refuse to go any further. Mason and Dixon recruited replacements, but on October 9 the surveying party came to a halt. “This day the Chief of the Indians,” recorded Mason in his journal, “informed us that the above mentioned War Path was the extent of his commission from the Chiefs of the Six Nations . . . [and] that he would not proceed one step farther westward.” After 233 miles, Mason and Dixon had reached the end of their survey.

As in years past, Mason and Dixon returned to Philadelphia, retracing their steps and marking the boundary line with wooden mile posts and cairns of stones on top of the Appalachian ridges. On Christmas Eve they met with the commissioners, who gave them the final assignment of producing a map and plan of the surveyed line. It took another eight months to deliver 200 copies of the desired record of their work. Finally, on September 11, 1768, nearly five years after they had arrived in Philadelphia, Mason and Dixon concluded their work and set sail for England and home.

After four years of surveying through the wilderness, Mason, left, and Dixon, center, mapped the boundary between Pennsylvania and Maryland at the Harlan family farm in Chester County. In this 2013 oil-on-canvas painting titled Drawing the Line, artist Adrian Martinez recreates the scene as it may have occurred in late 1767. Courtesy Adrian Martinez

Legacies

Charles Mason and Jeremiah Dixon reaped different rewards from their accomplishment. While both were well compensated, Dixon was feted by the Royal Society and amassed a considerable fortune before dying in January 1779 at the relatively young age of 46. Charles Mason received few of the scientific plaudits enjoyed by his partner. Embittered with the English scientific establishment’s refusal to make him a member of the Royal Society, he returned to America, intent on building a new life. But shortly after reaching Philadelphia, he died in October 1786, leaving behind his widow and seven children.

Less than 20 years after the completion of the Mason-Dixon Line, surveyors extended it to Pennsylvania’s western border. What had been a successful effort to settle an intercolonial dispute over land by drawing a line on the map quickly began to take on far greater significance. On March 1, 1780, the Pennsylvania legislature passed the Act for the Gradual Abolition of  Slavery. In no time at all, the Mason-Dixon Line morphed from a state boundary into a symbolic dividing line between slavery and freedom. By 1810 the number of slaves in the state had fallen from 6,855 to 795. The number of free blacks living in Pennsylvania in 1810 totaled 22,492. Across the border in Maryland, the enslaved population had grown to 111,502 by 1810. Free blacks accounted for an additional 33,927 of the state’s residents.

As slavery and its westward expansion increasingly dominated political discourse in the United States, the nation’s leaders first sought to resolve the issue by drawing more lines. The Missouri Compromise of 1820 essentially called for a continuation of the Mason-Dixon Line, extending it down the Ohio River from the 40th parallel to 36 degrees 30 minutes latitude and then stretching all the way to the Pacific coast. But reliance on imaginary lines drawn on the map was no more than a temporary salve to the growing antagonism between North and South. The inclusion of the new Fugitive Slave Act as a component of the Compromise of 1850 swept away the power of artificial boundaries such as the Mason-Dixon Line to provide sanctuary for those fleeing chattel slavery and sought to make all Americans complicit in the preservation of the South’s peculiar institution.

In this cartoon from Harper’s Weekly, January 7, 1860, a stern Miss Columbia oversees a rowdy classroom of Northerners and Southerners divided by the Mason-Dixon Line. A slate in the lower left corner refers to an “Irrepressible Conflict,” while the chalkboard behind the teacher has references to “UGRR” (Underground Railroad) and the South’s wish, “Let us alone.”
Library of Congress

The Christiana Riot in southern Lancaster County a few miles from the Maryland border vividly illustrated the changing circumstances. Alerted to the possible presence of four escaped slaves, Maryland slaveholder Edward Gorsuch and a posse showed up at the home of William Parker with warrants for the arrest of the four fugitives on September 11, 1851. After a two-hour confrontation, Gorsuch lay dead and his son Dickinson seriously wounded; the fugitives remained at liberty. A local jury’s failure to convict any of those arrested during the violent standoff established a new tone of armed defiance to the Fugitive Slave Act and was a preview of similar instances of defiance throughout the North in the ensuing decade.

The Christiana Riot demonstrated that by the mid-19th century, the Mason- Dixon Line represented a true dividing line between the industry, commerce, finance and increasingly polyglot population of the North and the hierarchical agrarian plantation society of the South. Pennsylvania had come to embody everything that the South would fight against. By crossing the Mason-Dixon Line to invade the state during the Civil War, Robert E. Lee sought more than a strategic advantage. He hoped to score a psychological victory by demonstrating the North’s vulnerability.

While Lee’s failure helped to seal the South’s eventual defeat, it failed to erase the power of the Mason-Dixon Line as a boundary with stark social consequences. The border remained a convenient delineation between the reality of the North’s triumph and an imagined past fashioned by Lost Cause myths conjured up to soothe the defeated South’s psyche. Until well into the 20th century, black passengers boarding the train in Pennsylvania had to move from integrated to segregated cars when crossing the border into Maryland. The solution to a colonial land dispute became, first, a symbol of the nation’s founding contradiction between freedom and slavery. Today it is better remembered as the subject of an engaging rock song.

For Further Reading

Edwin Danson’s Drawing the Line: How Mason and Dixon Surveyed the Most Famous Border in America (Wiley, 2001) provides an in-depth account of the survey and the science that informed
it. As an experienced geodetic surveyor, the author takes special pains to explain the astronomy that was central to Mason and Dixon’s achievement.

John H. B. Latrobe’s The History of Mason and Dixon’s Line (1855; reprint, Leopold Classic Library, 2017) and James Veech’s Mason and Dixon’s Line: A History (1857; reprint, Applewood Books, 2011) offer 19th-century perspectives. Despite its somewhat stilted style, Veech’s account adds valuable detail to the story.

Patrick Spero’s article “The Conojocular War: The Politics of Colonial Competition, 1732-1737,” Pennsylvania Magazine of History and Biography, October 2012, is a thorough academic examination of the war, its causes, consequences and major personalities.

For young readers, three books stand out. Judith St. George’s Mason and Dixon’s Line of Fire (Putnam, 1991) focuses on the violent encounters that characterized the Maryland–Pennsylvania border from Thomas Cresap’s depredations in the 1730s to the Whiskey Rebellion of 1794 and the collision of Union and Confederate armies at Gettysburg in July 1863. Sally M. Walker’s Boundaries: How the Mason-Dixon Line Settled a Family Feud and Divided a Nation (Candlewick, 2014) is a copiously illustrated recounting of the survey that includes valuable sidebars providing historical and scientific context. The first part of John C. Davenport’s The Mason-Dixon Line (Chelsea House, 2004) covers the survey, and the second part is devoted to the line’s history in the 19th and 20th centuries, with special insights into its symbolic importance as a boundary between the North and the South.

Rick Beard is an independent historian and museum consultant who writes frequently on the Civil War and other topics in American history.