The first iron bridge in the United States is believed to be the one erected by Trumbull in 1840 over the Erie Canal at Frankfort, N. Y. Record is also held of one of these bridges being built for the North Adams branch of the Boston & Albany Railroad, in 1846. About a year later, Nathaniel Rider began to build iron bridges for the New York & Harlem, the Erie, and some others of the early railroads. His bridges--of the truss type, of course, that type having been worked out in the timber bridges of the land--were each composed of cast-iron top-chords and post, the remaining part of the structure being fabricated of wrought-iron. The members were bolted together. Still, the failure of a Rider bridge upon the Erie in 1850, followed closely by the failure of a similar structure over the River Dee, in England, influenced officials of that railroad to a conclusion that iron bridges were unpractical, and to order them to be removed and replaced by wooden structures. For a time it looked as if the iron bridge were doomed. That was a dark day for the bridge engineers. A contemporary account says: "The first impulse to the general adoption of iron for railroad bridges was given by Benjamin H. Latrobe, chief engineer of the Baltimore & Ohio Railroad. When the extension of this road from Cumberland to Wheeling was begun, he decided to use this material in all the new bridges. Mr. Latrobe had previously much experience in the construction of wooden bridges in which iron was extensively used; he had also designed and used the fish-bellied girder constructed of cast and wrought-iron." Under the influence of the really great Latrobe, an iron span of 124 feet was built in 1852 at Harpers Ferry. In that same year, the B. & O. built its Monongahela River Bridge, a really pretentious structure of 3 spans of 205 feet each, and the first really great iron railroad bridge in all the land. The path was set. The conquest of iron over wood as a bridge material was merely a problem of good engineering. The iron bridge quickly came into its own. The Pennsylvania Railroad began building cast-iron bridges of from 65 to 110 feet span at its Altoona shops for the many creeks and runs along the western end of its line. The other railroads were following in rapid order. Squire Whipple, Bollman, Pratt--all the others who could design and build iron bridges--were kept more than busy by the work that poured in upon them.