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 a place on the Delmarva Peninsula which had been previously determined to be mid-way between the Atlantic Ocean and the Chesapeake Bay. Known as the Middle Point, it is now the southwest corner of the State of Delaware. From there they journeyed northward, proceeding with the painstaking task of surveying a line to intersect with a location 12 miles distant from the Town of New Castle. Temporary wooden markers were placed 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 this area to replace the temporary markers with stones imported from England. At intermediate mile points the stones were marked with the letters P and M on reverse sides. At every five-mile point the stones 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. The boundaries were formally approved in 1775.