Seisyllwg, kingdom of

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Seisyllwg, kingdom of. An early Welsh kingdom of obscure origin, though it may have been established by Seisyll ap Clydog, king of Ceredigion, by extending his dominion south to the Tywi valley (c.730). His descendant Angharad married Rhodri Mawr, who temporarily combined it with Gwynedd (871). Later (904), it was absorbed into the wider kingdom of Deheubarth under Hywel Dda; thereafter, Seisyllwg ceased to be an independent kingdom and its name fell into disuse.

Ralph Alan Griffiths