The Merthyr Tramway better known as the Penydarren tramway was opened in 1802, it was built by Dowlais, Penydarren and Plymouth Ironworks as a joint project. It was 9.5 miles in length and ran from Merthyr to Abercynon.
The line was immortalised by the running of the first ever steam train in 1804 by Richard Trevithicks locomotive. Trevithicks achievement is comemorated in a memorial erected in 1934 in Merthyr itself.
The route can be traced at the GR for this entry, with Bridges to be found at ST094962 and ST090965.