Richard Trevithick's locomotive made the first steam-hauled railway journey in 1804.
On 21 February 1804, Trevithick's high-pressure steam locomotive hauled a train of iron wagons and several passengers along the Penydarren tramway in Merthyr Tydfil, Wales. The journey covered about 9 miles (14.5 kilometres) and demonstrated that steam power could move heavy loads on rails.
The locomotive was built for Samuel Homfray's Penydarren ironworks. Although the demonstration was important, the locomotive was not a commercial success: its heavy weight damaged the cast-iron rails, which had originally been designed for horse-drawn wagons.
This event is often confused with the opening of the Stockton and Darlington Railway in 1825, the first public railway to use steam locomotives regularly. Trevithick's 1804 run came first, but it was an industrial demonstration rather than a public railway service.