Rhymney developed after the establishment of the Union ironworks in 1801, with the Rhymney Iron Company later being founded from a merger between the Bute and Union Ironworks in 1837. The ironworks used local coking coal, iron ore and limestone. From the mid-19th century, steam coal pits were sunk to the south of the town. The ironworks closed in 1891 and by the early 20th century the town's collieries employed nearly the entire local population.