One of the Medieval kingdoms of Wales.
Name derived from the Welsh deheu meaning of the south.
Created early in the 10th century by Hywel Dda through the fusion of the kingdom of Seisyllwg, inherited from his father Cadell ap Rhodri, with the kingdom of Dyfed, inherited from his father-in-law Llywarch ap Hyfaidd, to which he added effective dominion over the kingdom of Brycheinoig.
For the next two centuries alternated between periods of independence and unity with the kingdom of Gwynedd. In the 12th century entered a period of decline as it came under increasing pressure from the invading Normans. Ceredigion was transfered to Gwynedd and the kingdom effectively ceased to exist in 1236 following the death of Owain ap Gruffydd.