The Cornwall Railway, built to the 2.14 m (7 ft 0¼ in) broad gauge, ran from Plymouth to Falmouth. The section from Plymouth to Truro opened in 1859 when the Saltash Bridge was opened. The extension to Falmouth was completed in 1863. The original section remains open as part of the London to Penzance main line, the Truro to Falmouth line being operated as a branch. It was leased by the South Devon, Bristol & Exeter and Great Western Railways and in 1889, the Cornwall amalgamated with its three associate companies.

The Cornwall Railway viaducts were mostly built on stone piers but with spans of timber fans. This design was chosen by Isambard Kingdom Brunel in order to reduce the cost of their construction, but at the expense of high maintenance costs. The route crossed forty five rivers and deep valleys. Of these forty two were crossed by timber viaducts of various types. The remainder were the River Tamar at Saltash crossed on the Royal Albert Bridge, the River Fowey at Lostwithiel crossed by a low three-span viaduct (two spans being timber, the central one iron), and the river and canal at Par crossed on a five-arch low stone viaduct.

Replacement of the viaducts started in 1875 but led to a dispute between the Cornwall Railway and the Great Western Railway which leased the line. The lease precluded the conversion of the broad gauge line to standard gauge, and the Cornwall Railway refused to pay for the widening of the viaducts during rebuilding to accommodate a double line of standard gauge tracks (it had been built as a single-track line).

Following the amalgamation of the two companies on 1 July 1889, all the remaining viaducts were replaced, those between Saltash and St Germans being replaced by a deviation line, the remainder being either rebuilt in situ or having a replacement viaduct built immediately alongside. Because of this, many of Brunel's original piers still remain today.

The longest viaduct in Cornwall is at Truro. It was built of stone in 1904 and is 405 m (1,329 ft) long with sixteen arches and a maximum height of 26 m (86 ft). It was the last replacement of a Brunel viaduct. From the train, it provides a magnificent view of the city. Alongside it, fourteen of the original Brunel piers are still standing.