The place-name Ystradgynlais, meaning 'vale of the river Cynlais' – Cynlais may be a personal name, or derive from cyn ('chisel') and glais ('stream') – is first recorded in 1372.[5] In the 1600s there were only a couple of houses by the church and a pub (now the rectory). In 1801 there were only 993 residents in the town living in only 196 houses. The first documented written evidence of iron working in the area was at Ynyscedwyn and is of a deed of release dated 1729. By 1750 there were seven furnaces in south Wales, one of which was at Ynyscedwyn.
Tynycoed Chapel, located between Ynyswen and Penycae, near Ystradgynlais, was first constructed in 1774, and was rebuilt in 1829.[6]
The first written evidence of coal mining was at Wauclawdd in 1780. Most of the coal dug up was used in the blast furnaces of the ironworks. By 1790, the full extent of the mineral resources in the valley was better known and it was realised that to exploit these to the full, improved transport would be essential.
The greatest increase in the population was between 1821 and 1841. This coincides with the coming of George Crane and the development of the Ynyscedwyn Ironworks. By 1870, the town's industrial development was in decline due to various economic factors, although coal mining carried on in the area with a few light industries.
Culture
Parc yr Orsedd, YstradgynlaisThese remains were built in 1872 to house a planned steel mill. Although not completed, the site housed the Ynyscedwyn Tinplate Works
Ystradgynlais hosted the 1954 National Eisteddfod, an annual Welsh festival of literature, dance, and music. The century-old award-winning Ystradgynlais Public Band competed in the 2005 National Eisteddfod.[7]
Ystradgynlais is also home to the Miners Welfare Hall, known and promoted as 'The Welfare', which contains a cinema. In 2020 a Purple Plaque was installed at the building to mark Eunice Stallard's life and activity as a peace campaigner.[9]
It also has a number of public houses.
In 2016 The Stephen Lewis Tristars Aquathlon in Ystradgynlais won the Welsh triathlon event of the Year 2016.
Ystradgynlais has a bus station, served hourly by the First Cymru-operated X6 to and from Swansea, as well as the long-distance TrawsCymru T6 between Swansea and Brecon.[11]
In 1946, Smiths Industries Ltd, Ingersoll Ltd and Vickers Armstrong founded the Anglo-Celtic Watch Co. Ltd. producing watches on the Ynyscedwyn estate on the outskirts of Ystradgynlais. The factory was officially opened by Hugh Dalton on 15 March 1947. Vickers Armstrong sold their shares to the other two companies in 1948. The company became one of the largest producers of watches in Europe, producing up to 1.25 million watches a year until 1980 when it closed.[12][13]
