The cantilever bridge that carries the line from Edinburgh to Aberdeen of the former North British Railway over the Firth of Forth, 14 km west of Edinburgh, was one of the first major structures to be built of mild steel. The North British Railway planned to replace with bridges it ferries across the estuaries of both the Firth and the Tay on its route to the north. The Tay Bridge, to the design of Sir Thomas Bouch (1822-80) was completed in 1877 but disastrously collapsed in a storm two years later. Bouch was discredited, and preparations for a suspension bridge that he had designed to carry the railway over the Forth were abandoned.
The Forth Bridge Company (a consortium of railway companies in which the North British was pre-eminent) accepted a design for a steel cantilever bridge put forward by Sir John Fowler ((1817-98) and Sir Benjamin Baker (1840-1907), which was constructed from 1882 by Tancred & Arrol. The bridge was formally opened to traffic in 1890. It has a total length of 2.5 km and consists of three towers each made up of four steel tubes, 3.66 m in diameter, reaching a height of 110 m above high water, and braced with diagonal members. The ends of the landward arms rest on expansion roller beds on the granite towers. There are approach spans at each end of the bridge of conventional lattice girders resting on tapering granite piers. The central tower is built on an island, Inch Garvie, but the other two stand on concrete bases built in cassons in deep water. The bridge consumed 54,000 tonnes of steel and some 6.5 million rivets. At least 57 construction workers died during the course of its construction.
The bridge became a UNESCO world heritage site in 2015. There is interpretation at North Queensferry station and in Queensferry Museum.