The Pont de Sully, opened in 1877, comprises two elegant iron bridges which connect the Boulevard Henri-IV on the Right (north) Bank to the Ile Saint-Louis 1, and thence to the Saint-Bernard and Tournelle quays and the Boulevard Saint-Germain on the Left Bank.
The northern bridge crosses the small arm of the Seine with a cast iron central arch of 46m and two masonry arches of 15 m, while the southern bridge has three cast iron arches whose lengths are 46m, 49m and 46m.
The engineers were Paul Vaudrey and Gustave Brosselin.
The bridge was constructed by H. Joret et Cie., with castings from the founderies of the Cie. Terre-Noire at La Voulte et à Bessèges.
The above information is from the French Wikipedia entry.
Great attention was paid in moulding the castings of the outer ribs to present a smooth surface with fine detailing, although numerous small blowholes are visible. Some of the thin spandrel castings have suffered fractures. In some cases repairs have been carried out by welding on plates. It is difficult to obtain reliable welds on cast iron, and some failures are evident (e.g. photo 6).