The Three Sisters Bridges

The Three Sisters Bridges. Three Rivers Heritage Trail. , The three identical bridges spanning the Allegheny River are the only known example of a triple set of bridges constructed side-by-side across a major river. They were built between 1926 and 1928 when the War Department ruled that bridges over Pittsburgh's rivers had to be high enough not to interfere with river commerce in steel, coal and war materials during times of war. , , Their design is unique. They are self-anchoring suspension bridges-standing firmly on piers in the river and extending stiff girders out to meet the banks-but they are not anchored to the land. Their rigid eyebar chains are suspended from central towers and fastened to the end of giant girders that hold up the roadway. , , In 1926 the City Art Commission influenced the design of the first bridge, the Seventh Street Bridge, which was based on a rare example in Cologne, Germany. Pittsburgh's American Bridge Company built the bridge. The design reflected the Art Deco architectural style of the period. Within two years, identical spans were erected at Ninth and Sixth Streets. , , In 1928, The American Institute of Steel Construction voted the Sixth Street Bridge, now called the Roberto Clemente Bridge, the "most beautiful bridge" built in America that year. The Three Sisters are listed on the National Register of Historic Places for their significant engineering and technology.