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|- Succeeded by||Carmarthenshire|
Dinefwr was a local government district of Dyfed, Wales from 1974 to 1996. It was named after Dinefwr Castle which was the court of the House of Dinefwr and one of the three principal royal courts of Wales with Aberffraw and Shrewsbury.
It was formed by the merger of the borough of Llandovery, the urban districts of Ammanford, Cwmamman and Llandeilo along with Llandeilo Rural District, from the administrative county of Carmarthenshire. In 1996 the district became part the new county of Carmarthenshire.
Princely House of Dinefwr
With the death of Rhodri Mawr, the Kingdom of Gwynedd passed to his eldest son Anarawd ap Rhodri. Rhodri's second son Cadell ap Rhodri, however, looked outside Gwynedd's traditional borders and took possession of the Dark Ages Kingdom of Dyfed by the late 9th century, probably establishing his capital at the citadel of Dinefwr (first attested in 1161, but as a well-known stronghold).
King Hywel Dda united all of South Wales – the Deheubarth – in the early 10th century. The Dinefwr dynasty would rule in Deheubarth until their conquest by the Anglo-Normans in the 13th century. This branch would compete with House Aberffraw for supremacy and influence in Wales throughout the 10th, 11th, and 12th century, with Powys variously ruled between them. The Mathrafal clan who ruled Powys after the mid-11th century were a cadet branch of this family.