Seisyll ap Clydog was King of Ceredigion in

Wales Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...

some time in the late 7th or early 8th century. He gave his name to the later kingdom of Seisyllwg, which consisted of Ceredigion plus the region known as

Ystrad Tywi Ystrad Tywi (, ''Valley of the river Towy'') is a region of southwest Wales situated on both banks of the River Towy (), it contained places such as Cedweli, Carnwyllion, Loughor, Llandeilo, and Gwyr (although this is disputed). Although ...

; as such he was possibly the king responsible for the expansion. However, there is no contemporary evidence of this, and almost nothing is known of his life or reign.

History

Seisyll appears in the

Harleian genealogies __NOTOC__ The Harleian genealogies are a collection of Old Welsh genealogies preserved in British Library, Harley MS 3859. Part of the Harleian Library, the manuscript, which also contains the '' Annales Cambriae'' (Recension A) and a version of ...

for the kings of Ceredigion. Here, he is named as the son of Clydog or Clitauc Artgloys, and is the sixth in descent from

Ceredig Ceredig ap Cunedda (died 453), was a possibly fictional or at least not well attested in reliable sources king of Ceredigion in Wales.

, the traditional founder of Ceredigion. The Harleian also names him as the father of Arthgen, presumably the King of Ceredigion whom the ''

Annales Cambriae The (Latin for ''Annals of Wales'') is the title given to a complex of Latin chronicles compiled or derived from diverse sources at St David's in Dyfed, Wales. The earliest is a 12th-century presumed copy of a mid-10th-century original; later ...

'' record as dying in 807. Seisyll's name appears to derive from the notional

Late Latin Late Latin is the scholarly name for the form of Literary Latin of late antiquity.Roberts (1996), p. 537. English dictionary definitions of Late Latin date this period from the 3rd to 6th centuries CE, and continuing into the 7th century in ...

''*Saxillus'', which comes from the same root as the Welsh ''sais'', meaning

Saxon The Saxons, sometimes called the Old Saxons or Continental Saxons, were a Germanic people of early medieval "Old" Saxony () which became a Carolingian " stem duchy" in 804, in what is now northern Germany. Many of their neighbours were, like th ...

Englishman The English people are an ethnic group and nation native to England, who speak the English language, a West Germanic language, and share a common ancestry, history, and culture. The English identity began with the Anglo-Saxons, when they we ...

.Koch, p. 1602. Seisyll ap Clydog is generally taken to be the Seisyll for whom Seisyllwg was named. As such, historians such as

John Edward Lloyd Sir John Edward Lloyd (5 May 1861 – 20 June 1947) was a Welsh historian. Early life and eduction John Edward Lloyd was born in Liverpool on 5 May 1861. He was educated in the University College of Wales, Aberystwyth (which later become ...

and Egerton Phillimore believed that he was the king who founded that kingdom.Lloyd, p. 257 and note. However, contemporary sources continue to use the name Ceredigion for the realm of Seisyll and his successors. As such, "Seisyllwg" may represent a substantially later political development.

Notes

References

* * {{Rulers of medieval Wales History of Ceredigion Monarchs of Ceredigion