Arc Corner Monument
Near Wilmington, Delaware
That weathered granite post marks one of the strangest borders in America. Delaware's northern boundary is not a straight line. It is the arc of a circle, drawn with a radius of about twelve miles centered on the courthouse cupola in New Castle. It is often called the only true curved state border in the United States, a leftover from a seventeenth century land grant.
This particular stone, set in eighteen ninety-two, marks the Arc Corner, the exact point where that famous Twelve Mile Circle meets the top of a stretch called the Wedge and the long east to west line of the Mason and Dixon survey. A joint commission from Delaware and Pennsylvania hired the United States Coast and Geodetic Survey to triangulate the whole arc and plant markers every half mile. You are standing where three boundary lines collide, deep in the quiet woods of the White Clay Creek Preserve.
