With the building of the Transcontinental Railroad in late 1860's, the lack of a bridge across the Mississippi had become a major problem for the railroads.
Engineers pointed out that materials commonly used in bridge building could not support the wide span necessary to bridge the wide Mississippi river. Flooding would add stress to the breaking point. An all steel bridge could take the many stresses, but such a bridge was too expensive to build!
Andrew Carnegie pioneered a way to produce steel more cheaply for the bridge and formed the Keystone Bridge Co. to raise money to build the bridge.
The bridge was built at St. Louis, MO and is named for its designer and builder, James B. Eads. When completed in 1874, the Eads Bridge was the longest arch bridge in the world, with an overall length of 6,442 feet. The ribbed steel arch spans were considered daring, as was the use of steel as a primary structural material. This was the first such use of true steel in a major bridge.The cost of building the bridge was nearly $10 million ($210 million with inflation). Railway transport of goods then began to outstrip goods moved on waterways.