MERTHYR TYDFIL, or MERTHYR. TYDVIL, a parliamentary borough and market-town of Glamorganshire, South Wales, is situated in a bleak and hilly region on the river Taff, and on several railway lines, 25 miles north-north-west of Cardiff and 30 east-north-east of Swansea. The town, which consists principally of the houses of workmen, is for the most part meanly and irregularly built, and at one time, on account of its defective sanitary arrangements, was frequently subject to epidemics of great severity. Within recent years great improvements have taken place, and the town now possesses both a plentiful supply of pure water and an excellent system of sewage. There are also some good streets with handsome shops, while in the suburbs there are a number of private residences and villas inhabited by the wealthier classes. Apart from its extensive iron and steel works, the town possesses no feature of interest. It is situated in the centre of the South 'Wales coal basin, and the rich coal-mines in the vicinity supply great facilities for the iron industries. At Merthyr Tydfil, which is said to have received its name from the martyrdom of a British saint Tydfil, there were smelting-works at a very early period, but none of any importance until 1755. From about forty years ago until 1875 the manufacture of bar iron developed with great rapidity, but since then the production of steel has largely taken its place. The borough returns two members to parliament. The population of the urban sanitary district in 1871 was 51,949, and in 1881 it was 48,857; the population of the parliamentary borough, which includes the parish of Aberdare and parts of the parishes of Llanwonno and Merthyr Tydfil and of Vainor (Brecon), and has an area of 29,954 acres, was in the same years 97,020 and 91,347.