The Three Sisters Bridges

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 after 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: self-anchoring suspension bridges that stand on piers in the river and extend stiff girders out to meet the banks without being anchored to the land. Their rigid eyebar chains hang from central towers and are fastened to the ends of giant girders that support 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, and was built by Pittsburgh's American Bridge Company. 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 significance in engineering and technology.

Pittsburgh, Pennsylvania · United States