Still used as shorthand for separations between the north and south, the Mason-Dixon Line was for thousands of African Americans the point where they escaped from slavery into freedom. Established nearly a century before the Civil War, the boundary was also, for the time, an astonishing technical feat. Of 133 limestone markers laid to mark the border, which resolved a long-running, sometimes violent dispute between the Maryland and Pennsylvania colonies, only one is to believed to remain, undisturbed, in its original location. The original Crown Stone 40 and a replica dedicated in 2016 are in a farm field off Route 23 in Norrisville, about 8 miles east of I-83. (David Anderson, Baltimore Sun Media Group)