"The Menai Strait between the Isle of Anglesey and the mainland is spanned by the Britannia Bridge which was built originally by Robert Stephenson to carry the London to Holyhead railway line. His revolutionary design involved the use of wrought tubes over 400 feet in length and weighing 1500 tons, which were lifted hydraulically into position in 1849. Stephenson's bridge was an immediate success and survived until 1970 when wooden structures in the tunnel caught fire and almost completely destroyed the bridge. However it was re-built and now carries the main A55 Expressway above the original railway line, which is still in everyday use".

SOURCE:
Edwin Clark. The Britannia and Conway tubular bridges (London, 1850), plates vol., pl. II Artist George Hawkins.