Casselman River Bridge near Grantsville, Maryland – Built in 1813–1814 to carry the road across the Casselman River, it was the longest single-span stone arch bridge in the world at the time. Great Crossings Bridge near Confluence, Pennsylvania – Built in 1818 to carry the road over the Youghiogheny River, the bridge, and the adjacent town of Somerfield, Pennsylvania (which was razed) are under the waters of Youghiogheny River Lake (though still visible at times of extremely low water levels).[7]