Mason and Dixon's line

Mason and Dixon's line is the boundary separating Maryland from Pennsylvania and Delaware, and is the concurrent State line of Maryland and Pennsylvania. It is named after two eminent astronomers and mathematicians, Charles Mason and Jeremiah Dixon, who were sent out from England to run it. They started the survey in 1764 and did certain related works until 1767, however they completed the survey between 1703 and 1707, excepting thirty-six miles surveyed in 1782 by Colonel Alex. McLean and Joseph Neville. It is in the latitude of 39 deg. 43 min. 26.3 sec.

During the Civil War, it was inaccurately regarded as dividing the slave-holding from the free States, Maryland and
Delaware both recognising slavery.