Delaware’s boundaries were formed by three surveyed lines completed before it became a state in 1776: the 12-mile radius surveyed in 1701, the Transpeninsular Line surveyed in 1751, and the Mason-Dixon Line surveyed in 1763. These lines were created not to divide North and South, but to settle colonial land disputes after George Calvert, first Lord Baltimore, received the land that became Maryland in 1632, William Penn received land north of Maryland in 1681, and in 1682 the Duke of York granted Penn the Lower Counties on the Delaware, land also claimed under Baltimore’s charter. The dispute between the Penn and Calvert families began to take shape in 1731 with the Transpeninsular Line, which ran across the Delmarva Peninsula from Fenwick Island to the Chesapeake Bay; surveyed in 1751, it established a Middle Point that became Delaware’s southwest corner and the starting point for the north-south Tangent Line. Boundary stones of limestone from Doneshire, England, marked the line, with coats of arms every five miles and lettered stones at the other mile points. Delaware’s northern boundary, the 12-mile circle, originated in 1681 from William Penn’s grant and was surveyed in 1701 by Isaac Taylor and Thomas Pierson as an arc extending west from the Delaware River, though it was not approved by Pennsylvania until 1715 and by Delaware until 1719. To complete the north-south tangent line, Charles Mason and Jeremiah Dixon, recommended by royal astronomer James Bradley, arrived in Philadelphia on November 13, 1763, with advanced measuring and astronomical instruments. Beginning on June 18, 1764, they and a crew of 39 workers surveyed from the Middle Point northward to the place where the line intersected the 12-mile circle, then resurveyed back south to check their work, missing the Middle Point by only two feet, two inches. The north tangent line bisected the 12-mile circle at mile post 82, and from there the line was extended five miles farther north to latitude 39’43’ north, establishing the west line at marker 87, the in-state corner marker. Because the surveyed line crossed inside the arc, the bulge of the circle added 13 acres to Delaware.