The Mason-Dixon Line wasn’t created to divide North and South, but to settle a dispute between Colonial landowners

The Mason-Dixon Line, the iconic dividing line between North and South, is an invisible line running across the backyard of many Delawareans.

Charles Mason and Jeremiah Dixon’s milestone markers still dot the Maryland-Delaware-Pennsylvania border more than 240 years after they completed their survey.

Jutting out of the dirt on rural roadsides, highway medians and private property, the 81 original oolitic-limestone markers and sixreplacements run like a dotted line from nearDelmar to north of Newark.

This is the eastern-most leg of the legendary line immortalized in songs and movies and “Looney Tunes” cartoons, and the only chunk that is mainly vertical.

Rewind to 1763, when Mason and Dixon docked in Philadelphia, two English astronomer-mathematicians who came highly recommended by the director of the Royal Observatory at Greenwich. Their task: Discern the 233-mile border between William Penn’s land and Cecilius Calvert’s.

Geodetics, the present-day science that deals with measuring the Earth, was practiced mostly by ship’s captains and astronomers then. Measurements varied so wildly that some ships’ captains believed Philadelphia was actually part of Maryland. No one had ever measured a boundary so long that the Earth’s curvature would come into play.

“Today, it’s a no-brainer,” says Brian Cannon, historic interpreter at the New Castle Courthouse Museum. “You plug into a computer and it tells you just what to do, but back then, it required making some temporary lines, measuring a line on the ground, and then going back and adjusting that line based on what you know. It was a very math-heavy problem.”

Mason and Dixon’s job was to settle a three-generation-long boundary dispute between the Penns and the Calverts. Both families had been deeded land by British kings, but the deeds overlapped. The landlords had trouble collecting taxes from colonists because it was unclear who owned what. One colonist poked more than a dozen rifles through his log-cabin walls to protect his property. Ironically, less than eight years after the survey was finished, the American
Revolution would make it inconsequential.

Their line became shorthand for slave states and free states when it was mentioned on the floor of the U.S. Congress in raucous debates over the Missouri Compromise of 1820.

It became the invisible border between Southern culture and Yankee culture.

The differences weren’t just in the back of people’s minds; the train tracks above the line were a wider gauge than those below the line until 1886.

“It’s unlike any other boundary in the world,” says William E. Ecenbarger, who walked as much of the line as he could reach to write “Walkin’ the Line: A Journey From Past to Present Along the Mason-Dixon Line.”

“One is it’s a very famous geographic line with many, many historic significances, and the other is it’s a line that played a very symbolic role in the Civil Rights movement, even into the 1960s.”

Mason and Dixon started their work at a Colonial survey marker called Middle Point in the extreme southwestern corner of present-day Delaware. Take a road trip along Del. 54 in Sussex County and you’ll see this spot, just five miles west of Delmar. Look for four stones in a brick enclosure.

As they surveyed north and west, the duo measured distances with wrought-iron chains and surveyor’s instruments such as the transit – a combination compass-telescope that allowed them to take vertical and horizontal measurements. They used trigonometry to compute distances, heights and angles.

During the Delaware leg of the survey, they could have been spotted at the New Castle Courthouse or at St. Patrick’s Tavern in Newark, on the site of the present-day Deer Park Tavern. Most colonists wouldn’t single them out, though, because their names didn’t become well known until decades after their deaths.

Mason and Dixon trudged through flooded fields and cold creeks, and faced snakes and wild animals on their 233-mile trek with a team that included Native American guides, tent carriers, chain carriers and ax men, who cut trees to open up 24-foot to 27-foot paths called “vistas” so telescope sightings could be made.

Present-day Delaware is east of the Mason-Dixon Line, but it was once part of William Penn’s land, called the lower three counties along the Delaware. The present-day western border of the state divided Penn’s land and Calvert’s “Maryland.”

Mason and Dixon’s line is still accepted by the U.S. Geodetic Survey, and it became the model for British and American boundary makers. But the mathematicians had no idea their names would be commemorated for centuries to come when they boarded the Halifax Packet for the voyage back to England.

State officials and history buffs are combining efforts to protect the 81 original markers that remain along Delaware’s western border. One marker reportedly was removed and placed in a fireplace mantle. Another was uprooted for display at the 1904 St. Louis World’s Fair and went missing until the Marydel Lion’s Club found it and returned it to the boundary in 1964.