Penydarren Ironworks (Merthyr Tydfil)

The Penydarren Ironworks at Merthyr Tydfil in South Wales was the site of the most important single event in the prehistory of the railway — the construction and first operation of the world's first known steam locomotive to run on rails. Founded by ironmaster Samuel Homfray in 1784 as an integrated iron-making works, Penydarren was one of several major ironworks in the Merthyr Tydfil area that collectively made the town the iron-making capital of the world in the late eighteenth and early nineteenth centuries, its furnaces and rolling mills producing the iron that built the industrial revolution.

In 1803–04, following a wager between Homfray and a neighbouring ironmaster, Richard Trevithick designed and the Penydarren works built a high-pressure steam engine mounted on a wheeled carriage intended to haul iron along the works' Merthyr Tramroad to the Glamorganshire Canal at Abercynon — the world's first railway locomotive. The engine made its historic journey on 21 February 1804, hauling ten tons of iron and seventy men over nine and three quarter miles, winning Homfray's bet and demonstrating for the first time that a steam engine mounted on wheels could move itself and a useful load along an iron track by friction alone. The locomotive proved too heavy for the cast-iron plateway rails and was converted to a stationary engine, but the demonstration that smooth wheels on smooth iron rails could provide traction was the foundational proof from which the entire railway age followed.

The Penydarren Ironworks continued in production until 1859, its working life spanning the very years during which Trevithick's 1804 proof-of-concept was developed into the practical railway by Hedley, Stephenson, and their successors. The site is commemorated at Cyfarthfa Castle Museum in Merthyr Tydfil, and a full-size working replica of the Penydarren locomotive operates at Locomotion at Shildon.