�The Britannia Tubular Bridge. Entrance from the Bangor Side�, Wales, c 1848.

UNITED KINGDOM - JUNE 04: Tinted lithograph by John Ambrose. The Britannia Tubular Bridge was designed by Robert Stephenson (1803-1859) and was completed in 1850. It was constructed to provide trains of the Chester and Holyhead Railway with a passageway across the Menai Straits from mainland Wales to Anglesey. Stephenson�s solution to the problem of how to carry the weight of trains pulling multiple carriages across the straits was to construct the bridge from rectangular iron tubes, through which the trains would run. The railway terminated at Holyhead, which became a major port for travellers to Ireland. The stone lions carved by John Thomas, a pair of which guide either end of the bridge, are clearly visible in the picture. (Photo by SSPL/Getty Images)