The early Kingdoms of Ceredigion, Seisyllwg and Deheubarth
Ceredigion
The Kingdom of Ceredigion was one of Welsh Kingdoms that emerged in 5th-century, it was originally part of the territory governed by Cunedda after he had warded off Irish invaders and granted the land to his son Ceredig (Ceretic) as his own kingdom in 424, and it was named after him. Ceredigion meaning "the people of Ceredig." The earliest form of the kingdom's name may have been Ceretica.
Situated along the western coast of Wales, its area corresponded roughly to that of the modern county of Ceredigion which includes modern towns of Aberaeron, Aberystwyth, Cardigan, Lampeter, Llanddewi brefi, New Quay, and Tregaron and it is where the rivers Severn and Wye have their source. The Cambrian Mountains covered much of the east of the Kingdom and its hilly geography made it difficult for foreign invaders to conquer. As a coastal Kingdom, its creation was a very good strategic move as it sealed the vulnerable coastal gap between Dyfed and Gwynedd, thus preventing any further Irish gains in Wales. It was bordered by the Kingdoms of Gwynedd, Powys and Dyfed, the River Teifi formed the border with Dyfed for part of its length.
c.424 - 453 Ceredig Fifth son of Cunedda
In Ceredig's later years, when the kingdom is under threat of attack by Irish raiders and he is advised to abdicate in favour of his young grandson, Carannog, who is horrified at the prospect and flees the court later becoming St Carannog. According to tradition he is also the grandfather of St David.
453–490 Usai
490–525 Serwyl
525–560 Boddw
560–595 Arthfoddw
595–630 Arthlwys
630–665 Clydog I
Seisyllwg
Seisyll, embarked on a series of conquests and added the three cantrefs of Ystrad Tywy to Ceredigion, the enlarged Kingdom of Seisyllwg being named after him. Note that the dates given for the reigns of Seisyll and his immediate descendents must be treated with caution, as they are are educated guesses. The only secure date we have is for the death of Gwgan derived from the Annales Cambriae.
665 - c.700 Seisyll ap Clydog. Seisyll conquered Ystrad Towy (most of modernday Carmarthenshire), taking it from Dyfed. The enlarged kingdom of Ceredigion, which by then also included the Gower Peninsula, is renamed the kingdom of Seisyllwg in his honour
c.700 - c.735 Arthwyr ap Seisyll
c.735 - c.770 Dyfnwal ap Arthwyr
c.770 - c.807 Meurig ap Dyfnwal
by 800 The kingdoms of Buellt and Gwerthrynion are taken by Seisyllwg
c.808 - 872 Gwgan ap Meurig
872 Gwgon drowned while crossing the River Llychwr in Gower whilst chasing off a Viking raid, leaving no heir. Gwgon's sister, Angharad, was married to Rhodri the Great of Gwynedd, who became steward over Gwgon's realm. While this gave Rhodri no standing to press a claim to 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, giving Rhodri control of much of north and central Wales, and from this point onwards, Seisyllwg is ruled by a branch of the kings of Gwynedd as a sub-kingdom.
878 Cadell ap Rhodri confirmed King of Seisyllwg, upon the death of Rhodri Mawr,
904 Cadell ap Rhodri and his son, Hywel Dda, conquer Dyfed
911 Cadell died and Seisyllwg was divided among his two sons, Hywel Dda and Clydog
Deheubarth
920 Clydog died in 920, leaving the whole of Seissylwg to Hywel, who quickly merged Seisyllwg and Dyfed into the new kingdom of Deheubarth, which covered most of southwest Wales. From this power base, he later went on to unite almost all of Wales
950 The death of Hywel Dda, king of all Wales, leaves the country divided. Hywel's sons, Owain, Rhun, Rhodri and Edwyn, take possession of his estates in South Wales, with Rhodri becoming king of Deheubarth itself and Owain becoming prince of Ceredigion.
952 - 953 As part of the ongoing conflict between Deheubarth and Gwynedd, Owain leads an army into the North Wales Kingdom and engages its men at the Battle of Aberconwy. The fighting is so fierce that both sides are forced to withdraw, having sustained heavy losses. The following year, Gwynedd repays the compliment, invading and devastating Ceredigion, before being driven out by more fierce fighting.
957 Owain succeeds to the throne of Deheubarth and Ceredigion is fully reunited with it under him as its single ruler.