Robert Stephenson's pioneering wrought and cast iron tubular bridge at Conwy carried the main railway line from London to Holyhead. Stephenson recognised the importance of Conwy Castle and the walled town of Conwy and tried to blend the portals of the railway bridge with the Castle. The castellated portals and the facing on the support wall on the left of the picture are made from blocks of Carboniferous limestone from a nearby quarry.