Charles Mason, a fellow of the Royal Society and noted astronomer, and his sometime assistant, land surveyor and amateur astronomer, Jeremiah Dixon, were hired by certain wealthy interests in what was then the British colony of America to conclude a number of difficult boundary disputes in the young colonies.
Landing in Philedelphia in 1763, Mason and Dixon spent the next four years painstakingly measuring and fixing the proper boundaries between the various colonies, ceasing their work on October 18, 1867. (A team of their subordinates completed the survey in 1787.)
The lines they laid down, although resurveyed since that time, formed the basic lines of the borders between the colonies (and later the states) of Delaware, Maryland, Pennsylvania and West Virginia. Later, as these states took different sides in the Civil War, the line came to symbolise the political and cultural border between the southern and northern states.