The Coraopolis Bridge is a girder bridge over the back channel of the Ohio River connecting Grand Avenue on Neville Island to Ferree Street in Coraopolis, Pennsylvania. It opened in 1995 to replace a structure of historic significance. The original Pratt/Bowstring/Pennsylvania through truss spans, designed by Theodore Cooper, were formerly the (third) Sixth Street Bridge, spanning the Allegheny River, in downtown Pittsburgh, and were built in 1892 by the Union Bridge Company. They were floated downstream by the Foundation Company in 1927 rather than being demolished when the bridge was removed to enable construction of the present (fourth) Three Sisters (Pittsburgh) Sixth Street Self-anchored suspension bridge. However, by the late 1980s, the old bridge could no longer support traffic volumes and was replaced by a newer structure. The Sixth Street bridges Note: Material from this section is adopted from the HAER report on this bridge. The through truss spans incorporated in the present Coraopolis Bridge were originally erected across the Allegheny River at Sixth Street in Pittsburgh, linking Pittsburgh with the main business thoroughfare of neighboring Allegheny City. This was the third of four bridges to serve that location, which is considered among Pittsburgh's most important river crossings. The growth of Pittsburgh was strongly influenced by its numerous waterways, and the successful linking of the city with its neighboring communities by means of bridges was a significant factor in the development of its metropolitan identity. Allegheny City was annexed by Pittsburgh in 1907, becoming the city's "North Side". First Sixth Street Bridge The first bridge to cross the Allegheny at Sixth Street was a six-span, flat-roofed, covered wooden bridge constructed in 1819. This bridge had a total length of , consisting of four spans, a span, and a span. The design and construction of this bridge have traditionally been attributed to a Mr. Lothrop; it was presumably a Burr arch truss, like the Ninth (Hand) Street Bridge, another of Lothrop's products. Physical evidence for this assumption survived until the 1890s, when an observer reported that the skewbacks from the wooden arches remained visible in the north abutment. Second Sixth Street Bridge In 1860, a wire-suspension bridge, designed by John A. Roebling, replaced the decaying timber structure. This bridge was four spans long, with two main spans, and approach spans measuring each. The bridge was dominated by cast iron towers, each formed by four cast iron columns. Although the Roebling bridge,