Merthyr Tramroad Tunnel (Trevithick's Tunnel)

Cadw's description

Summary description and reason for designation

The following provides a general description of the Scheduled Ancient Monument.

The monument comprises the remains of the Merthyr Tramroad Tunnel. It is situated at Pentrebach and forms an important element in the nineteenth century Merthyr (or Penydarren) tramroad. The Merthyr tramroad was built in 1793 and ran from the ironworks of Merthyr Tydfil to the Glamorganshire Canal at Abercynon. The tramroad ceased to be used in about 1880. It was carried in a tunnel under the charging area of the blast furnaces of the Plymouth Ironworks at Pentrebach. The tunnel measures about 110m in length, 2.44m in height and 2.57m in width. In 1830, the tunnel was subsequently extended to the south, the new section measuring about 70m in length, 3.96m in height and 3.96m in width.

The great Railway Era was the product of two distinct lines of development: the growth of tramways and the appearance of the locomotive steam engine. These were first brought together, albeit in a tentative manner, by Richard Trevithick. On the 21st of February 1804, Richard Trevithick's high-pressure steam engine travelled the Merthyr Tramroad, passing through the tunnel on its way to Abercynon. It pulled five wagons, containing ten tons of iron (the haulage of which was intended to discharge a substantial wager) and seventy passengers (the great majority of whom being last-minute opportunistic day-trippers) - and was the world's first journey by a passenger carrying railway locomotive. To achieve this, the existing double line of tramplates was removed from the tunnel and replaced by a single line below the centre of the arch. However, the brittle cast iron tram-plates used on the Merthyr tramroad had been designed for horse-drawn traffic and broke under the weight of the locomotive. After several further journeys (and many more damaged tramplates), the experiment was abandoned and the engine, deprived of its wheels, put to use in the foundry.

The monument is of national importance for its potential to enhance and illustrate our knowledge and understanding of the development of the transport network associated with the iron industry. The importance of the monument is further enhanced by the survival of detailed historical documentation and its association with the early railway pioneer, Richard Trevithick.

The area scheduled comprises the remains described and an area around them within which related evidence may be expected to survive.