Kingdom of Seisyllwg: Map & History

Later history and merger with Dyfed

In 872, Gwgon, the last in the traditional line of kings of Ceredigion, drowned, leaving no heir. Gwgon's sister, Angharad, was married to Rhodri Mawr (Rhodri the Great) of Gwynedd, who became steward over Gwgon's realm. While this gave Rhodri no standing to claim kingship himself, he was able to install his and Angharad's younger son, Cadell, as the new King of Seisyllwg. Cadell ruled as a vassal to his father, and later, to his elder brother Anarawd, who established the House of Dinefwr.

After Cadell's death in 911, Seisyllwg was divided among his two sons, Hywel (later known as Hywel Dda, or Howel the Good), and Clydog.

Origins

It is unclear when Seisyllwg emerged as a distinct unit. It is assumed to have been named for Seisyll ap Clydog, King of Ceredigion in the 7th or early 8th century, and as such he is traditionally regarded as its founder. Seisyll appears in the Harleian genealogies for the Kings of Ceredigion, but no early sources attribute the foundation of Seisyllwg to him, and the name Ceredigion continues to be used into the 9th century. The name Seisyllwg appears in some later sources, such as the Book of Llandaff, the Welsh Triads, and the Welsh laws, the latter of which describes it as one of the three principal subdivisions of South Wales, along with Morgannwg and Reinwg (probably Dyfed).