Its unique design consists of two 455-foot (138.7 m) lenticular iron trusses 100 feet (30.5 m) above the water, with conventional plate-girder approach spans.

It has attracted sightseers since its construction and has appeared in many paintings, photographs, guidebooks, postage stamps and on the UK £2 coin.

The other, the 'coastal' scheme, was a line with many engineering difficulties but which could serve the important naval town of Devonport and the industrial area around St Austell.

The Cornwall Railway applied for an Act of Parliament in 1845 but it was rejected, in part because of William Moorsom's plan to carry trains across the water of the Hamoaze on the Devonport-to-Torpoint Ferry.

Following this Isambard Kingdom Brunel took over as engineer and proposed to cross the water higher upstream using a bridge at Saltash instead.

Brunel was present when Stephenson raised the girders of his Britannia Bridge across the Menai Strait in the same year.

[3] From 1849 to 1853 Brunel was erecting an iron bridge of his own; the Chepstow Railway Bridge carried the South Wales Railway across the River Wye and featured a main truss of 300 feet (91 m) with a curving tubular main member and three conventional plate-girder approach spans of 100 feet (30 m), a similar solution to that adopted for crossing the River Tamar at Saltash.

[7] The two spans are lenticular trusses with the top chord of each truss comprising a heavy tubular arch in compression, which tend to expand in length under load, while the bottom chord comprises a pair of chains, which tend to contract in length under load.

This in turn enables each of the trusses to be supported with no horizontal thrust exerted on the piers, which is crucial in view of the curved track on either side.

The fee he sought for building the Saltash Bridge was £162,000, but on 21 September 1855 while constructing the first of the two trusses he filed for bankruptcy.

[4] The landward piers on the Cornish side of the river were completed in 1854 and the girders for these spans were hoisted up to their correct positions.

Now that it was completed, the bridge had its statutory inspection and tests by Colonel Yolland on behalf of the Board of Trade on 20 April 1859.

Several thousand spectators attended that day, although guests from Cornwall were late for the ceremony as their train broke down at Liskeard.

[5] After Brunel's premature death on 15 September 1859 the directors of the Cornwall Railway Company decided to make the bridge a memorial to him by adding the words I.K.

During the 1930s new cross-bracing and diagonal sway-bracing were added between the vertical standards to further strengthen the bridge and keep the suspension chains hanging in the correct shape.

[7] In 2011 Network Rail began a three-year £10 million refurbishment involving replacing 50,000 bolts and installation of 100 tonnes of new steelwork.

The bridge has also been stripped back to the bare metal and repainted in the Goose Grey colour originally applied in 1952.

[4] During its construction it was photographed many times and after its opening it was the subject for many paintings, including those by Devonport-born artist Alfred Wallis.

[17] John Betjeman summed up its impact on the traveller: The general grey slate and back gardens of Plymouth, as seen from the Great Western made the surprise of Saltash Bridge all the more exciting.

Hundreds of feet below, the pathetic steam ferry to Saltash from the Devon bank tried to compete with Brunel's mighty bridge.