National Register Listing

Delaware Boundary Markers

a.k.a. Transpeninsular Line;Mason-Dixon Line;Tangent Line;The Arc;T

State boundary lines between DE-MD/DE-PA, Not Applicable, DE

When Charles Mason and Jeremiah Dixon completed their boundary survey between the Penn and Calvert proprietaries, their report represented the most sophisticated mathematical work every accomplished on the North American continent to that date, 1768. The remarkable accuracy of their survey is testimony to the high development that had been reached by scientific instruments.

Politically, the boundary lines represent an important turning point in the history of Delaware. Until the western boundary of the three lower counties (Delaware) was finally established, large tracts remained vacant for want of clear title. When the boundary was finally settled, the land in lower Delaware west of tidewater could be confidently developed.

Mason and Dixon's report, when it was accepted, resolved the long-standing conflict between the two proprietaries, and ended a court battle that had begun in 1682, with the issuance of William Penn's vague royal charter. Because both proprietors could construe their charters to include much of the same territory, both colonies claimed jurisdiction over Sussex County, Delaware, parts of the northern counties of Delaware, and the territory around the present Maryland-Pennsylvania boundary.

The boundary markers survive today in a remarkably good state of preservation. Most of the original stones still are in place; at some points, they are preserved in public parks, but most can be found along hedgerows or in the woods. A very few of them have been mistreated, moved, or defaced. Others have been lost and replaced with newer markers. The historical societies of Delaware, Pennsylvania and Maryland have each preserved crown-stones in their museums; these removed stones have been replaced with replicas.

Local significance of the district:
Listed in National Register of Historic Places in 1975.