Saving the Mason-Dixon Line

By Bijal P. Trivedi
National Geographic Today
April 10, 2002

Most Americans know the Mason-Dixon Line as the divider between North and South; freedom and slavery. But the line's origins have nothing to do with slavery and actually predate the United States.

The line is, in fact, the result of a bloody land dispute between proprietors of Pennsylvania and Maryland when the country was just a collection of British colonies.

Yet the very stones that mark this infamous boundary are weathering, damaged, vandalized or missing altogether. For the last ten years, two surveyors, Todd Babcock and Dilwyn Knott, armed with a passion for American history and a Global Positioning System (GPS) are locating and documenting each and every stone laid by Charles Mason and Jeremiah Dixon more than 200 years ago.

"We're losing (the stones) at an increasing rate so it's very important that we obtain the precise location of each stone so we can go back and repair damaged stones and replace lost ones," says Todd Babcock, president of the Mason-Dixon Line Preservation Partnership (MDLPP).

"I think Mason and Dixon are lost in the history. Something that we hope to do, is to tell people a little bit about Charles Mason and Jeremiah Dixon," Babcock says. "They weren't some senators who debated slavery on the House floor. They were surveyors and astronomers."

Mason was an astronomer employed by The Royal Society in Greenwich, England. He spent his time observing the stars and the moon, and establishing lunar tables that could be used to determine longitude.

Dixon was a surveyor from Cockfield in Durham County in England, and was educated by John Bird, a renowned maker of high precision astronomical instruments.

In 1763, Mason and Dixon landed the monumental task of resolving an 80-year property dispute between the Calvert family of Maryland and Penn family of Pennsylvania, and were asked to lay stone markers indicating the boundary.

The boundary began at 15 miles south of the southern most tip of the city of Philadelphia and followed a constant latitude west to a point between western Pennsylvania and what we now call West Virginia. GPS measurements taken by Babcock and Knott, a member of MDLPP, reveal that the line was off the mark by as little as one inch in some places and never more than 800 feet.

Mason and Dixon used the stars to calculate this path through the wilderness and mark out the 233-mile-long boundary line between Pennsylvania and Maryland, and the 83 miles long north-south boundary between Maryland and Delaware; the effort took five years.

The stones—huge blocks of limestone between 3.5 and 5 feet long and weighing between 300 and 600 pounds—were quarried in Southern Great Britain and shipped to America.

Carried by wagon to their final resting place on the line, the stones were placed at one-mile intervals. Mile markers were decorated with vertical fluting and a P on the north face and M on the southern face; every fifth mile along the line the stones were engraved with the Penn coat of arms on the Pennsylvania side and the Calvert coat of arms on the other.

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