Forth Bridge (1890): Scotland's Great Cantilever Railway Bridge

The Forth Bridge is a steel cantilever railway bridge across the Firth of Forth, the broad estuary west of Edinburgh in Scotland. Opened on 4 March 1890, it was designed by Sir John Fowler and Sir Benjamin Baker after the Tay Bridge disaster had shaken public faith in railway bridges. With its two record-breaking main spans and striking red silhouette, it became an icon of Victorian engineering and in 2015 was declared a UNESCO World Heritage Site.

Background: the Firth of Forth and the Tay disaster

In the nineteenth century, rail travellers between Edinburgh and the north of Scotland had to cross the Firth of Forth and the Firth of Tay by ferry or make long detours inland. Rival railway companies competed for this traffic and wanted direct routes.

The engineer Thomas Bouch designed bridges for both estuaries. His Tay Bridge opened in 1878, and work began on his Forth design, a suspension bridge. On the night of 28 December 1879, during a violent storm, the central spans of the Tay Bridge collapsed as a train was crossing. Everyone on board died; about 75 people are thought to have been on the train, of whom 59 have been identified. The inquiry found the bridge had been badly designed, built and maintained, with too little allowance for wind. Work on Bouch’s Forth bridge was abandoned.

Design: a bridge that looks strong

The Forth Bridge Railway Company turned to Fowler and Baker, who proposed a cantilever design in steel, a material only recently produced in large quantities by new processes. A cantilever is a beam supported at one end; here, three huge double cantilevers rise from piers in the water, and their arms reach out towards each other, with short suspended girders linking them.

The structure was designed to resist wind pressure far greater than Bouch had assumed, and its massive tubes and lattice girders were meant to look as strong as they were. To explain the principle, Baker staged a famous demonstration in which two men sat on chairs with their arms outstretched, holding sticks braced against the chairs, supporting a third person sitting on a plank between them. The central figure in the photographed version was Kaichi Watanabe, a Japanese engineer studying in Britain.

Construction

Work began in 1882 under the contractors Tancred, Arrol & Co., led by the Glasgow engineer William Arrol. The three main towers stand on foundations at North and South Queensferry and on the small island of Inchgarvie in the middle of the Firth. Workers sank caissons, giant watertight chambers filled with compressed air, to build some of the foundations in the riverbed.

At its peak, more than 4,000 men worked on the bridge. The work was dangerous: men fell from great heights, were hit by falling objects or drowned, and some suffered from “caisson disease”, now called decompression sickness. The official death toll recorded at the time was 57. In the 2000s a local memorial committee researched the records and identified more than 70 men who died as a result of the work.

The cantilevers were built out from the towers until they met in late 1889. On 4 March 1890 the Prince of Wales, the future Edward VII, opened the bridge by driving in a final gilded rivet.

Legacy

The bridge gave Edinburgh a direct rail link to Fife, Dundee and Aberdeen, especially once the Tay had also been rebridged in 1887. It still carries trains today, with around 200 crossings a day.

Its two main spans, each 521 metres (1,710 feet), were the longest in the world until the Quebec Bridge in Canada opened in 1917, and it remains one of the longest cantilever bridges ever built. The phrase “like painting the Forth Bridge” became a British expression for an endless task, although a modern coating applied between 2002 and 2011 is expected to last for decades.

In 2015 UNESCO inscribed the bridge as a World Heritage Site, describing it as a milestone in bridge design. It stands beside the Forth Road Bridge of 1964 and the Queensferry Crossing of 2017, so three centuries of bridge engineering can be seen side by side. Other landmarks of the same era include New York’s Brooklyn Bridge, while the Forth Bridge’s iron and steel predecessors go back to the Iron Bridge at Coalbrookdale.

By the numbers

Timeline

• 1878, 1 June: Bouch’s Tay Bridge opens.
• 1879, 28 December: The Tay Bridge collapses in a storm.
• 1881: Plans for Bouch’s suspension bridge over the Forth are abandoned.
• 1882, December: The contract for the Fowler and Baker cantilever bridge is signed.
• 1887: Baker’s “human cantilever” demonstration is photographed.
• 1889, November: The cantilevers are joined across the Firth.
• 1890, 4 March: The Prince of Wales opens the Forth Bridge.
• 2015, 5 July: The bridge is inscribed as a UNESCO World Heritage Site.

Why it matters

The Forth Bridge restored confidence in large railway bridges after the Tay disaster and showed what steel could achieve. It remains a working railway bridge, a symbol of Scotland and one of the best-known structures of the industrial age.