Note: It was the boundary between Maryland and Pennsylvania in the pre-Civil War period in the United States. Together with the Ohio River, it formed the dividing line between slave states to the south and free states to the north. It was the 233-mile-long line that was originally surveyed along the parallel 39043" in 1763-1767 by two Englishmen, Charles Mason and Jeremiah Dixon. The original purpose was to settle the long-disputed boundaries of the overlapping land grants of the Penns of Pennsylvania and the Calverts of Maryland. The term "Mason and Dixon Line" was first used in congressional debates surrounding the Missouri Compromise (enacted in 1820).