Mason and Dixon's Line

Mason and Dixon's Line is popularly supposed to have been a line dividing the slaveholding from the non-slaveholding states, and to have run due east and west. In reality it ran for more than one-third of its length between two slave states, Maryland and Delaware, and a small part of it is an arc of a circle. It was run by two English engineers, Charles Mason and Jeremiah Dixon, between the years 1764 and 1767, for the purpose of settling the disputed boundaries between Maryland on the one side and Pennsylvania and Delaware on the other. Their instructions were to begin at the most easterly point on the Atlantic Ocean, and run due west to a point midway between the Atlantic and the Chesapeake Bay; thence northward, so that the line should become a tangent to the north-western boundary of Delaware, which was a circle described from New Castle Court-house as centre, with a radius of 12 miles. The line was then to follow the curve in a westerly direction until it reached a point due north of the point of tangency; thence due north until it intersected a line run due west from a point 15 miles south of Philadelphia; and thence due west until it intersected a line running due north from the most western source of the Potomac River. The work was done with such skill and accuracy that a revision in 1849, with instruments of much greater precision, disclosed no error of importance.