Smithfield Street Bridge in Pittsburgh, PA. A National Historic Landmark, this lenticular truss was constructed in 1883 to cross the Monongahela River. It features a combination of iron and steel and stands as an elegant example of its bridge type. It is the oldest steel truss in the United States. (source: National Register of Historic Places Nomination Form, Donald C. Jackson, 1975)
(Used by permission, David Anthony, 2004)