Ystradgynlais is on the banks of the River Tawe in southwest Powys. The town, which is the largest in the historic county of Brecknockshire and the second largest in the administrative area of Powys, grew around the ironmaking, coal mining and watchmaking industries.

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. 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 Ystradgynlais living in only 196 houses. The first documented written evidence of iron working in the area was at nearby Ynyscedwyn (NPRN 34037) and is of a deed of release dated 1729. By 1750 there were only seven furnaces in south Wales, one of which was at Ynyscedwyn. The first written evidence of coal working dates from 1780, coal being sent to the blast furnaces. After the full extent of the area's mineral resources became better known,the town developed rapidly with the expansion of the coal and iron industries during the nineteenth and early twentieth centuries.
Source:
https://en.wikipedia.org/wiki/Ystradgynlais

RCAHMW, 21 July 2017