Today marks the one-year Anniversary of this website, Twelve Mile Circle. However I’ve yet to explain the actual Twelve Mile Circle behind the name. I promised myself I would do so if I could keep this site active for a year, and I’ve now met that goal. So here goes.
As many regular readers already guessed, it refers to the arc that forms the preponderance of the border between Delaware and Pennsylvania. I find it particularly fascinating. Borders often follow straight lines formally delineated by surveyors. Other times they rely upon natural phenomena such as rivers, ridgelines, or coasts. Imagine, though, the sheer wackiness of a boundary based on a circle.
Yes, a Circle
This image gives a pretty good overview of the border between the two states. Clearly it forms a perfect arc. This one happens to have a 12-mile radius. Notice the little red dot at New Castle that marks the exact center. This unusual arrangement has roots in colonial times. Very simply put, the Duke of York was granted all lands within a circle of twelve miles surrounding New Castle. Eventually he conveyed his Delaware holdings to William Penn. For some reason he keep these lands distinct from Pennsylvania even though they were now both part of his domain. The circle survived.
At the Center
This is the exact center of the circle. It’s the old courthouse in New Castle (map). Specifically it’s the cupola right at the top of the courthouse. The circle may have been well-defined by land records but it’s precise measurement on the ground was problematic due to its unusual shape. The 22.57 mile arc has been surveyed several times including 1710 by Taylor and Pierson and again in 1892-1893 by modern surveyors using more sophisticated techniques.
Imagine the challenge of surveying this border. Rather than tracking a straight line, the surveyors needed to account for an infinite number of twelve-mile spokes emanating from New Castle.
In an upcoming post I’ll go into further detail on the numerous anomalies of the Delaware border. This is just a brief introduction of one aspect. Perhaps you’ve already noticed another anomaly (hint: look immediately to the left of the border arc). Stay tuned!
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