Merthyr Tydfil, sometimes known as Merthyr Tudful, is a Welsh industrial town and county borough. It was named after Tydfil the Martyr, a 5th-century Welsh Christian princess who was killed there. The county borough encompasses both sides of the River Taff’s deep valley, as well as the surrounding high hills. The county borough of Merthyr Tydfil is centred on the town of Merthyr Tydfil, which stretches north into the Brecon Beacons National Park. The ancient county of Glamorgan (Morgannwg) encompasses the majority of the county borough, including the town of Merthyr Tydfil, but it also contains some region in the north that is part of the old county of Brecknockshire (Sir Frycheiniog). The town’s current expansion was founded on four big ironworks constructed after 1757. In Merthyr Tydfil, Richard Trevithick developed the world’s first steam locomotive in 1804. Coal mining supplemented the ironworks, especially after 1841 when railways replaced the late-eighteenth-century Glamorganshire Canal as the primary mode of transport to Cardiff. The Dowlais ironworks were the world’s largest by 1850. Coal mining in the area progressively ended after 1918, and the last remaining local steelworks, at Dowlais, closed. Merthyr Tydfil’s industrial renaissance began during World War II, and the town currently produces a wide range of products, including Hoover washing machines. It is a significant shopping centre that also provides regional services. The grounds of Cyfarthfa Castle (1825), a former ironmaster’s castle that now houses a museum, are now home to a public park.