Work on the Cockermouth, Keswick & Penrith Railway got underway in May 1862, with the first goods train testing the trackwork in October 1864.

The line crossed Mosedale Beck, two miles east of Threlkeld, on a 12-arch stone viaduct, a little over 140 yards long. It was constructed to carry a single track but was extended northwards in 1900 when this section of line was doubled. The trackbed rises on a 1 in 62 gradient towards Penrith.

Since the structure was widened, three of the piers have been reinforced in concrete.

Despite the line suffering heavy losses in the 1950s and being earmarked for closure in Beeching’s 1963 report, the Penrith-Keswick passenger service survived until 1972.

In 1997, the BR Property Board agreed not to move forward with proposals to demolish Mosedale Viaduct. A proposal to reinstate the line as far as Keswick is being progressed and some political support has been garnered.