The Mason-Dixon Line
Created | Updated Jun 7, 2013
The line runs along the southern border of Pennsylvania with the (now states) of Virginia and Maryland, then along the eastern border of Maryland with Delaware.
During the years before the Civil war, the line served as a divider between slave states and free states (at least on the eastern sea-board). All of the states above the Mason-Dixon were free states and had no slavery, and all of the states south of the line were slave states. Thus, if an escaping slave could cross that line (into Pennsylvania or Delaware) he would be relatively safe, especially among the Amish and Quaker people's of Southern Pennsylvania.
People such as Harriet Tubman and other conductors on what is called the "Underground Railroad" would take groups of slaves to freedom across this line, where they would then move on to other points north.
Today, the line serves as a sort of boundry between states that are considered "the south", and states that are considered "the north".