The South Wales Valleys () are a group of industrialised peri-urban valleys in South Wales. Most of the valleys run northsouth, roughly parallel to each other. Commonly referred to as "The Valleys" (), they stretch from Carmarthenshire in the west to Monmouthshire in the east; to the edge of the pastoral country of the Vale of Glamorgan and the coastal plain near the cities of Swansea, Cardiff, and Newport. History Until the mid-19th century, the South Wales valleys were sparsely inhabited. The industrialisation of the Valleys occurred in two phases. First, in the second half of the 18th century, the iron industry was established on the northern edge of the Valleys, mainly by English entrepreneurs. This made South Wales the most important part of Britain for ironmaking until the middle of the 19th century. Second, from 1850 until the outbreak of the First World War, the South Wales Coalfield was developed to supply steam coal and anthracite. The South Wales Valleys hosted Britain's only mountainous coalfields. Topography defined the shape of the mining communities, with a "hand and fingers" pattern of urban development. There were fewer than 1,000 people in the Rhondda valley in 1851, 17,000 by 1870, 114,000 by 1901 and 153,000 by 1911; but the wider impact of urbanisation was constrained by geography—the Rhondda remained a collection of villages rather than a town. The population of the Valleys in the late 19th and early 20th centuries was disproportionately young and male; many of them were migrants drawn from other parts of Wales or from further afield. The new communities had extremely high birth rates—in 1840, more than 20 per cent of Tredegar's population was aged under seven, and Rhondda's birth rate in 1911 was 36 per thousand, levels usually associated with mid-19th century Britain. Merthyr Tydfil, at the northern end of the Taff valley, became Wales's largest town thanks to its growing ironworks at Dowlais and Cyfarthfa. The neighbouring Taff Bargoed Valley to the east became the centre of serious industrial and political strife during the 1930s, especially in and around the villages of Trelewis and Bedlinog, which served the local collieries of Deep Navigation and Taff Merthyr. The South Wales coalfield attracted huge numbers of people from rural areas to the valleys; and many rows of terraced housing were built along the valley sides to accommodate the influx. The coal mined in the valleys was transported south