Mason and Dixon's Line is usually thought of as the line that divides the North and the South. Actually it is the east-west boundary line that separates Pennsylvania from Maryland and part of West Virginia, and the north-south boundary between Maryland and Delaware. Before the Civil War, the southern boundary of Pennsylvania was considered the dividing line between the slave and nonslave states.

In the 1700's, a boundary quarrel arose between Pennsylvania and Maryland. The two agreed to settle the dispute by having the land surveyed. In 1763, they called in two English astronomers, Charles Mason and Jeremiah Dixon. They completed their survey in 1767. The line was named after them.

The surveyors set up milestones to mark the boundary. Through the years, souvenir hunters removed many stones and used them as doorsteps and curbstones. However, authorities recovered many of these stones and replaced nearly all the stolen markers. Occasionally a dispute arose as to the exact location of the line. But surveys made in 1849 and 1900 showed there was no important error in the line Mason and Dixon decided upon. A survey during the 1960's resulted in a slight shift of the line, which is now at 39 degrees 43 minutes 19.521 seconds north latitude.

SOURCE: IBM 1999 WORLD BOOK