Around 1765, which two English surveyors drew a line separating the southern slave states from the northern free states?

The famous boundary line was established between 1763 and 1767 by two English surveyors, Charles Mason and Jeremiah Dixon. They were originally hired to resolve a long and often violent border dispute between the colonies of Maryland and Pennsylvania. The conflict over land grants awarded to the Calvert and Penn families had raged for decades. Using advanced astronomical techniques for the time, Mason and Dixon meticulously charted a 233-mile line at a latitude of 39°43' N, settling the territorial claims once and for all.

This carefully surveyed border only later acquired its famous significance as the dividing line between slavery and freedom. The transformation began after Pennsylvania passed a law for the gradual abolition of slavery in 1780. As a result, the southern border of the state, the very line Mason and Dixon had drawn, became the informal boundary between free and slave-holding states.

The term "Mason-Dixon Line" entered popular use during the congressional debates for the Missouri Compromise of 1820, which further solidified its role as the demarcation between the North and the South. What started as a solution to a colonial property dispute evolved into a powerful symbol of the deep cultural and political divisions over slavery that would ultimately lead to the Civil War.