In the process of building the Stockton and Darlington Railway, the world's first publicly subscribed passenger railway, as well as then the longest in the world, several rivers needed to be crossed by the railway line. One of these, over the Gaunless River near Aukland in modern-day County Durham, was designed by George Stephenson as the first railway bridge to be made of iron. It was built over the following two years, and opened on 25 September 1825. It remained in use until 1901, and has since become part of the collection of the National Railway Museum at York.
Editors. "First Iron Railroad Bridge". The Literary Encyclopedia. First published 30 August 2013
[http://www.litencyc.com/php/stopics.php?rec=true&UID=408, accessed 23 January 2017.]