CAERPHILLY, Glamorganshire, Wales, 7m. from Cardiff, and 6m. from Pontypridd. The origin of the name is unknown. It was formerly in the ancient parish of Eglwysilan, but from that and Bedwas, Mon., an ecclesiastical parish was formed in 185o, while the whole of the parishes of Eglwysilan and Llanfabon were in 1893 constituted into an urban district; its population in 1931 was 35,76o. The ancient commote of Senghenydd (corresponding to the modern hundred of Caerphilly) comprised the mountainous district from the ridge of Cefn On on the south to Breconshire on the north, being bounded by the rivers Taff and Rhymney on the west and east. Its inhabitants, though nominally subject to the lords of Glamorgan since Fitzhamon's conquest, often raided the lowlands. To keep these in check, Gilbert de Clare, during the closing years of the reign of Henry III., built the castle of Caer philly on the southern edge of this district, in a wide plain between the two rivers. Prince Llewelyn ap Griffith laid siege to it in 1271. Subsequently completed, it became "the earliest and the most complete example in Britain of a concentric castle of the type known as `Edwardian'." The great hall is a fine example of Decorated architecture. This and other additions are attributed to Hugh le Despenser (1318-26). It was attacked by Owain Glyn Dwr in 1403. Before the middle of the 15th century it had ceased to be a fortified residence and was used as a prison, but its ruins at the present day are extensive and imposing.
The town grew up around the castle but never received a charter or had a governing body. Its markets during the 19th century were chiefly noted for the Caerphilly cheese sold there. The dis trict was one of the chief centres of the Methodist revival of the 18th century, the first synod of the Calvinistic Methodists being held in 1743 at Watford farm close to the town. With the develop ment of the south Wales coal-field the prosperity of Caerphilly greatly increased. In 1858 was opened the Rhymney railway from Rhymney to Caerphilly and on to Taff's Well, whence it had running powers over the Taff Vale railway to Cardiff, but in 1871, by means of the Cefn On tunnel a direct line was made to Car diff. A branch line, 4m. long, was opened in 1894 to Senghenydd. The Pontypridd and Newport railway was constructed in 1887, and there is a joint station at Caerphilly for both railways. Trade depression since 1921 has had especially marked effects in this locality.