MERTHYR TYDFIL or MERTHYR TYDVIL, munic ipal, county and parliamentary borough, of Glamorganshire, S.
Wales, situated on the river Taff and the Glamorganshire Canal, and served by the G.W.R. and L.M.S.R., 2 m. N.W. of Cardiff. Pop. (1931) 71,099. It is said to have derived its name from the martyrdom of St. Tydfil, daughter of Brychan, put to death by Saxons in the 5th century. Three miles to the north on a lime stone rock rising 470 ft. are the ruins of Morlais Castle, built about 1286 by Gilbert de Clare on the northern limits of his lord ship of Glamorgan. The town is irregularly built and owed its early industrial prosperity to the abundant ironstone of the dis trict. Four great iron works were established here between 1759 and 1782. With the earliest, that of Dowlais, the Guest family were associated. In 1765, Cyfarthfa was started by Anthony Bacon and sold in 1794 to Richard Crawshay. The Plymouth works were started soon after Cyfarthfa, by Wilkinson and Guest. They were closed down in 1882, but the collieries belonging to them continued to be worked. The fourth great ironworks were
those of Pen-y-darran which were carried on from 1782 to 1859. It was at Dowlais (in 1856) that Bessemer steel was first rolled into rails, but the use of puddled iron was not wholly abandoned at the works till 1882. The use of the local coal for smelting gave a great impetus to the iron industry. The Dowlais Company work collieries and have since 1891 a branch steel and iron works on the coast near Cardiff. Industrial depression after the World War seriously affected the coal, iron and steel trades. Cyfarthfa was converted into steel works in 1883. The iron ore used latterly has been mainly imported from Spain. Merthyr Vale is mainly depen dent on coal-mining. In 185o, the town had a local board of health; in 1894, an urban district council; in 1905, a corporation; in 1898, a county borough. In 1832, it was given one member and a second in 1867.