Eads Bridge is a combined road and railway bridge over the Mississippi River connecting the cities of St. Louis, Missouri and East St. Louis, Illinois. It is located on the St. Louis riverfront between Laclede's Landing, to the north, and the grounds of the Gateway Arch, to the south. The bridge is named for its designer and builder, James Buchanan Eads.
Opened in 1874, Eads Bridge was the first bridge erected across the Mississippi south of the Missouri River. Earlier bridges were located north of the Missouri, where the Mississippi is smaller. None of the earlier bridges survive; Eads Bridge is the oldest bridge on the river.
At 520 feet between the piers, the center arch of Eads Bridge was the longest rigid span ever built at the time of its construction (only a few suspension bridges had longer spans). It remained the longest rigid span until the completion of the 525 foot (160 meter) arch of Gustave Eiffel's Maria Pia Bridge, in Porto, Portugal, in 1877.
Extending more than 100 ft below water level, the foundations for Eads Bridge were the deepest underwater constructions of their time. They were installed using pneumatic caissons, a pioneering application of caisson technology in the United States and, at the time, by far the largest caissons ever built. The Eads Bridge caissons were the model for subsequent projects including the Brooklyn Bridge which was constructed just a few years later.
During construction, the partially-completed arches were suspended from above, on cables rigged to temporary wooden towers which were erected on top of the piers. This procedure avoided the need for temporary supports standing in the river and is sometimes cited as the first use of the "cantilever principle" for a large bridge.
In addition to its age and size, Eads Bridge is noted for the material used in its construction. Much of the metal in the bridge is wrought iron but the primary load-carrying components of the arches were made from steel. This was the first large-scale application of steel as a structural material and initiated the shift from wrought-iron to steel as the default material for large structures.