Twelve-Mile Circle

The Twelve-Mile Circle is an arc that makes up most of the boundary between the Commonwealth of Pennsylvania and the State of Delaware in the United States.

It is a circle with a twelve-mile radius, with the center of the circle in the center of the town of New Castle, Delaware. In 1750, the center of the circle was fixed at the cupola of the courthouse in New Castle. The Twelve-Mile Circle continues into the Delaware River. A small portion of the circle, known as the "Arc Line," also forms part of the Mason-Dixon line, separating Delaware and Maryland. The Twelve-Mile Circle is the only territorial boundary in the United States that is a true arc (excluding all boundaries defined by latitude and longitude, like much of the border between the US and Canada, which—when viewed with the North Pole as the center—are all also arcs).

Its existence dates from a deed to William Penn from the Duke of York on August 24, 1682, which granted Penn:

The fact that the circle extends into the Delaware River makes for an unusual territorial possession. Most territorial boundaries that follow watercourses split the water course between the two territories by one of two methods, either by the midpoint of the watercourse (the Grotian Method, after Hugo Grotius) or, more often, midpoint of the main flow channel, or thalweg. However, due to the text of the deed, within the Twelve-Mile Circle, all the Delaware River to the low-tide mark on the east (New Jersey) side is territory of the state of Delaware.

New Jersey has often debated this claim, as the rest of its territorial boundaries along the Delaware River are determined by the Thalweg method. The dispute has been brought to the Supreme Court of the United States on three occasions (all titled New Jersey v. Delaware), most notably in 1934 [ [ "State of New Jersey v. State of Delaware", 291 US 361] ] , and also in 1935 [ [ "State of New Jersey v. State of Delaware", 295 US 694] ] and 2007. The court's opinion for the first case contains an extensive history of the claims to this territory, and the second memorably [The state of Delaware, [is] perpetually enjoined from disputing the sovereignty, jurisdiction, and dominion of the state of New Jersey over the territory adjudged to the state of New Jersey by this decree; and the state of New Jersey, [is] perpetually enjoined from disputing the sovereignty, jurisdiction, and dominion of the state of Delaware over the territory adjudged to the state of Delaware by this decree.] enjoins New Jersey and Delaware from ever disputing their jurisdictions again.

Regardless of the Supreme Court's admonition to the two states against further litigation on this subject, they were back before the court as late as November 2005, when New Jersey's desire to approve plans by BP to build a liquefied natural gas terminal along the New Jersey shore of the Delaware River fell afoul of Delaware's Coastal Zone Act. [cite web
title=NJ to file lawsuit against Delaware over Delaware River jurisdiction
publisher=Philadelphia Business Journal
date=July 28, 2005
] The court on January 23, 2006, appointed a special master to study the border dispute, a process likely to take years. [cite web
title=DE Receives Favorable Recommendation in U.S. Supreme Court Dispute with NJ over Regulation of Wharves on the Delaware River
publisher=Connolly Bove Lodge & Hutz LLP
month=April | year=2007
] Meanwhile the Delaware House of Representatives considered a (symbolic) bill to call out the National Guard to safeguard the State's interests, while New Jersey legislators made comments about the Battleship New Jersey, moored upriver from the site. [Search archives of [] for "BP gas terminal dealt setback", January 24, 2006]

urveying the Circle

There is a persistent rumor that David Rittenhouse, the famous astronomer and instrument-maker of Pennsylvania, surveyed the circle around New Castle, but this is likely not correct. The circle was first laid out by surveyors named Taylor and Pierson in 1701. [Thomas D. Cope, "Some Local Scholars Who Counselled the Proprietors of Pennsylvania and their Commissioners during the Boundary Surveys of the 1760's," "Proceedings of the American Philosophical Society", vol. 99, no. 4 (August 1955), pp. 268-276, p. 275.] The 1813 "Memoirs of the life of David Rittenhouse" by William Barton surmises that Rittenhouse was involved in such a survey in 1763, based on a letter in which Rittenhouse mentions being paid "for my attendance at New Castle," but there is no clear record of what, exactly, Rittenhouse was paid for. His biographer, Brooke Hindle, guesses that Rittenhouse assisted with latitude or longitude calculations. [Brooke Hindle, "David Rittenhouse", Princeton University Press, 1964, pp. 20-21.]

ee also

* The Wedge
* Transpeninsular Line
* Mason-Dixon line


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