Charged with marking the long-disputed boundaries of the colonies of Maryland and Pennsylvania, including the Three Lower Counties of Delaware, English astronomers Charles Mason and Jeremiah Dixon landed in America on November 15, 1763. The following June they traveled to the Middle Point on the Delmarva Peninsula, then the place determined to be midway between the Atlantic Ocean and the Chesapeake Bay and now the southwest corner of the State of Delaware. From there they journeyed northward, surveying a line to intersect with a location 12 miles distant from the Town of New Castle, and placed temporary wooden markers at one-mile intervals. On July 6, 1764, they arrived here, fifteen miles north of their place of beginning. In December 1765 they returned to replace the temporary markers with stones imported from England. Stones at intermediate mile points were marked with the letters P and M on reverse sides, and stones at every five-mile point were engraved with the coats of arms of the Calvert and Penn families, proprietors of the colonies. Mason and Dixon completed their work in January 1768, and the boundaries were formally approved in 1775.