Glen Rock, Pennsylvania

You are crossing the most famous border in American history, and it was drawn to settle an argument between two rich families. In the 1600s, the Calvert family held the charter for Maryland and the Penn family held Pennsylvania. The problem was that Maryland's 1632 charter granted territory up to the 40th parallel, but Pennsylvania's 1681 charter described its southern border using the same language differently. If Maryland's claim held, Philadelphia would have fallen inside Maryland. After eighty years of legal warfare and armed skirmishes between settlers, both families hired Charles Mason, an English astronomer, and Jeremiah Dixon, a surveyor, to settle it. Between 1763 and 1767, Mason and Dixon surveyed 244 miles at latitude 39 degrees 43 minutes north, defined as exactly fifteen miles south of the southernmost point in Philadelphia. They placed limestone crownstones shipped from England every five miles and smaller markers every mile. They stopped when their Iroquois guides refused to continue into Lenape territory. The line became famous for something Mason and Dixon never intended. After Pennsylvania abolished slavery in 1781, this east-west survey line became the de facto boundary between free states and slave states. During the Missouri Compromise debates of 1820, the Mason-Dixon Line entered the national vocabulary as the dividing line between North and South. It still is.