(WHTM) – Along the boundary between Pennsylvania and Maryland, both states have a number of markers about a number of markers. Welcome to the Mason-Dixon line.

In 1763 Charles Mason and Jeremiah Dixon began surveying the boundary between Pennsylvania and Maryland to settle a dispute between the proprietors of the two colonies; the Penn family in Pennsylvania, and the Calvert family in Maryland. The argument over the exact location of the border had been festering for 82 years, and required pressure from the crown to coax the two parties to an agreement.

Mason and Dixon placed a marker stone every mile, with M on one side, and P on the other. Every five miles they would erect a Crown stone, with the coat of arms of the Penn family on the Pennsylvania side, and the coat of arms of the Calvert family on the Maryland side.

Their survey included the boundary between Maryland and Delaware, which at the time was part of Pennsylvania. The stones at the center of the Delmarva Peninsula, from which they started their measurements, are still there. (From Route 50 in Maryland you travel a few miles east on Route 54, if you’re interested in taking a look.) The crown stone here actually shows four coats of arms-Penn on north and east, and Calvert on west and south.

Another interesting marker is located where the curved northern boundary of Delaware meets with the east-west boundary line-the one everyone thinks of as “the” Mason-Dixon line. Determining this exact point got a little messy; this stone wasn’t erected until the 1920s.

The survey made things awkward for some landowners. The Mary Penn Bed and Breakfast is in Pennsylvania. It’s also the Mary Penn Bed and Breakfast in Maryland. The Mason-Dixon Line bisects the house, passing through the center hallway. And yes, the property owners pay taxes to both states.

By the time Mason and Dixon finished their work in 1767, they had surveyed over 240 miles of boundary line and placed over 220 stones. Over the years markers have worn down, been damaged, or lost. In some locations replica markers have been set-here at the Crown Stone mile 40 marker we see a replica next to the worn-down nub of the original.

The Mason-Dixon survey remains one of the most accurate in history. Follow-up surveys over the years show some of their measurements were off just a few hundred feet – at most. But these trivial inaccuracies have not been corrected. The line laid out by Mason and Dixon is still the official boundary between Maryland and Pennsylvania.