RHONDDA (formerly Ystradyfodwg), an urban district and parliamentary division of Glamorganshire, South Wales. It is 12 m. long by about 434 m. across at its widest part, and comprises two main valleys, named after their respective rivers, Rhondda Fawr (912 m.) and Rhondda Fach, or the lesser (612 m.), running S.E. and S.W. respectively till their junction at Porth, and thence the single valley for upwards of a mile farther down the boundary of the Pontypridd urban district at Trehafod. The valleys are narrow and tortuous, and their lateral boundaries are formed by steep hills varying in height from about 560 ft. on either side of Trehafod to 1340 ft. on the N.E. of:Maerdy in the lesser Rhondda and 1742 ft. on the S.W. of Treherbert in the main valley, while the mountains at the upper end of the latter valley culminate in Carn Moesen (1950 ft.). The two valleys are separated by the steep ridge of Cefn-rhondda, which ranges from 600 ft. high above Porth to 1690 ft. near the upper end of the district. There are a few tributary valleys of which Cwmparc, Clydach Vale and Cymmer are the chief. Though the urban district measures 23,884 acres, the area built upon is generally a narrow strip on either side of each river except at Treorky and Ton, where the valley of the Rhondda Fawr opens out a little. In 1877 the ancient parish of Ystradyfodwg (with the omission of the township of Rhigos, which lies beyond the mountains to the north) was formed into an urban district bearing the parish name, the area having previously been part of a rural district under the Pontypridd rural sanitary authority. In October 1879, portions of the parishes of Llanwonno and Llantrisant, comprising over 5000 acres, were added to the urban area, the whole being consolidated in 1894 into one civil parish. In 1897, the name of the urban district was changed into Rhondda. The Taff Vale railway runs up each of the two valleys from a junction at Porth (16 m. N.W. of Cardiff), and has five stations in the main valley and four in the lesser one. From Porth it runs to Pontypridd, whence there is communication with Cardiff, Barry and Newport. The Rhondda and Swansea Bay railway (authorized in 1882, opened in 1890, and now worked by the Great Western) connects the upper end of the main valley, where it has a station, Blaen-rhondda, with Port Talbot, Neath and Swansea (31 m. distant) by means of a line which has a tunnel 3443 yds. long.
The district occupies almost the centre of the eastern division of the South Wales coal-field, and its coal, upon which the inhabitants are almost entirely dependent, is unsurpassed for its steam-raising properties. In common with other East Glamorgan coal it became commercially known as Cardiff coal from the fact that Cardiff was at first its only port of shipment. The development of the Rhondda coal-field was later in date than those of Aberdare and Merthyr, and it received its chief impetus from the American Civil War. Thus the population of the parish (excluding Rhigos), which was 576 in 1811, 951 in 1851 and 3035 in 1861, increased to 16,914 in 1871. When the boundaries of the district were extended in 1879 the population of the enlarged area was calculated by the registrar-general to be 23,950 in 1871, but it reached 55,632 in 1881, and 113,735 in 1901, showing an increase of 104% in the previous twenty years. In 1901, 35·4% of the population of three years of age and upwards spoke English only, 11·4% spoke Welsh only, the remainder being bilingual.
Ecclesiastically the parish of Ystradyfodwg was an ancient chapelry dependent on Llantrisant. The old parish church at Ton Pentre (in substitution for which a new church was built in 1893–94) served the whole parish till past the middle of the 19th century. Between 1879 and 1900 the ancient-parish (excluding Rhigos) was divided into seven ecclesiastical parishes, the six new ones being Llwyn-y-pia (1879), Tylorstown (1887), Ynyshir (1887), Treherbert (1893), Cwmparc (1898) and Ferndale (1900). The additional area brought into the urban district in 1879 comprises two other ecclesiastical parishes, Cymmer and Porth (1894), and Dinas and Penygraig (1901). These nine parishes, comprised in the urban district, have twenty churches and eighteen mission-rooms, with accommodation for about 12,000 persons. This area, together with Pontypridd, Glyntaff and Llanwonno, form the rural deanery of Rhondda in the archdeaconry and diocese of Llandaff. There wer! at the end of 1905 over one hundred and fifty nonconformism chapels and mission rooms, with accommodation for over 85,000 persons, of which provision nearly two-thirds was in chapels with Welsh services. There is a Roman Catholic church at Tonypandy. The public buildings include the council house and offices of the district council, erected in 1883–84 for the local board at Pentre, libraries and workmen's institutes at Ystrad (1895), and Cymmer (1893), Maerdy (1905), Dinas (1893), and Ferndale public halls, the property of a private company at Treherbert (1872), and Tonypandy (1891) and a county intermediate school at Porth. By means of a tunnel about 2100 yds. long water is obtained for the greater part of the main valley from the lake of Llyn Fawr on the Neath side of the mountain range which shuts in the valley on the north. This lake has been converted into a storage reservoir of about 167 million gallons capacity. The rest of the district is supplied from the Pontypridd Water Company’s works above Maerdy in the lesser valley.
The ancient parish (excluding Rhigos) was formed into a parliamentary constituency with one member in 1885. The present urban district substantially corresponds to the ancient territorial division of Glyn-rhondda, one of the four commotes of the cantred of Penychen, and subsequently, in Norman times, one of the twelve “members” of the lordship of Glamorgan. Its Welsh lords enjoyed a large measure of independence and had their own courts, in which Welsh law was administered down to 1535, when the lordship was fully incorporated in the county of Glamorgan. On the ridge of Cefn-rhondda between the two valleys was the Franciscan monastery of Penrhys, famous for its image of the Virgin and for its holy well which attracted large pilgrimages. It was dissolved about 1415, probably owing to its having supported Glyndwr in his rebellion. Edward II. came here from Neath Abbey and was captured on the 16th of November 1326, either at Penrhys, or between it and Llantrisant. (D. Ll. T.)