Why the Mason Dixon Survey Started on Philly’s South Street
Historical marker for the Mason-Dixon Survey at the foot of South Street in Philadelphia. Photo by Jim Murphy, author of Real Philly History, Real Fast.
Today, most people know the Mason Dixon Line as the boundary between the country’s North and South.
But that was never the intention of the Mason-Dixon survey. Nor did the Mason Dixon Line become famous until 57 years after the survey began.
The survey was originally ordered by the British Crown to end a longstanding border dispute between the Calvert family of Maryland and the Penn family of Pennsylvania – a dispute that led to frequent skirmishes and bloodshed. The two colonies shared the cost of the survey.
Mason and Dixon traveled from England to Philadelphia in 1763 to mark the northern border of Maryland, defined in 1732 as being “15 miles south of the most southerly part of Philadelphia.”
Because William Penn’s original city of Philadelphia ended at present-day South Street (originally Cedar Street), Mason and Dixon started there to find the southernmost house in the city.
Today, that house would be in the middle of I-95, somewhere near the South Street Pedestrian Bridge.
(Left) The Plumsted house, photographed in 1901, where the Mason-Dixon survey began in Philadelphia. (Right) The South Street pedestrian bridge today.
With their starting point marked, Mason and Dixon moved 15 miles south, then began cutting a 24-to-30-feet-wide-vista across rugged Pennsylvania woodlands. A team of about 115 men was required for this backbreaking work.
To mark the boundary, the men placed 500-lb. crownstones with the Penn and Calvert families’ coats of arms every five miles. Smaller stones were placed every mile.
It was only after the Missouri Compromise of 1820 that states north of the line became known as “free” states and those south if it “slave states.” Ironically, neither Mason nor Dixon’s name was on the survey report.
The original border dispute drove William Penn to hurry back to England in 1684, just two years after arriving at his city of Philadelphia.
His biggest concern: learning that Philadelphia was being called “the prettiest town in Maryland.”
Fortunately for the Penn family, the Crown resolved that problem in 1760, ordering Lord Baltimore to accept a previously signed 1732 agreement placing Philadelphia 15 miles north of the border.
And that’s why the Mason Dixon survey starts in Philadelphia.
Jim Murphy’s new book, “Real Philly History, Real Fast” is available from Temple University Press, bookshop.org and amazon.com.