In the late 1950s and early 1960s the BBC broadcast a series of television programmes called Railway Roundabout. These programmes featured many lines which were later closed and locomotives that were about to disappear forever. Filmed in colour and black and white and produced to professional broadcast standards these titles have stood the test of time and are a real insight into the Steam Era in Britain in the 50s and 60s.
The extract shown above was broadcast in 1959 and shows film of both the Monmouth to Ross and Monmouth to Chepstow lines and was uploaded to YouTube in 2011. The Penallt viaduct is seen in a clip starting at about 3:29.