Dictionary of National Biography, 1885-1900/Cadell (d.909)
CADELL (d. 909), king of Ceredigion and afterwards of Powys, was one of the six warlike sons of Rhodri Mawr, the most powerful of the early Welsh kings. If we can trust a late authority, he was Rhodri's eldest son, and received as his patrimony Ceredigion, with the palace at Dinevwr, and an overlordship over his other brothers. In 877 Rhodri was slain by the Saxons, and Cadell entered upon his turbulent reign. In conjunction with his brothers he ravaged and devastated the neighbouring states of Dyved and Brecheiniog to such purpose that the latter gladly accepted the help of King Alfred against a nearer and more terrible foe (Asser, M. H. B. 488 B.C.) Not long after the sons of Rhodri were compelled themselves to become Alfred's men (? 885. Mr. J. R. Green's ‘Conquest of England,’ p. 183, dates the submission of the house of Rhodri in 897). The harmony between the brothers did not long survive their defeat. In 894 Anarawd, the king of Gwynedd, joined the English in a devastating inroad into Cadell's territory, and burnt remorselessly all the houses and corn in Dyved and Ystrad Towy (Annales Cambriæ, Gwentian Brut). Soon after Rhodri's death Cadell is said to have driven his brother Mervyn out of Powys and added it to his possessions (Gwentian Brut, 876); but as Mervyn continued alive until 903 (An. Cambr. MS. B), and was still styled king of Powys (Gwentian Brut, which puts his death in 892), it is very improbable that a lasting conquest was effected. Anyhow, as Anarawd continued to reign in Gwynedd, Cadell certainly was not, as the ‘Gwentian Brut’ asserts, thus made king over all Wales. Indeed, it is quite probable that Anarawd was the elder of the sons of Rhodri. Besides civil feuds and Saxon invasions the period of Cadell's reign was signalised by repeated invasions of the ‘black pagans,’ as the Welsh called the Irish Danes, which culminated in 906 in the destruction of St. David's. Three years afterwards Cadell died (909 A. C. MS. A, 907 B. y T., 900 Gwentian B.) Three of his sons are mentioned by the chronicles, Howel, Clydog, and Meurug. Of these the eldest became Cadell's successor, and was celebrated as Howel Dha, the wisest and best of the Welsh kings.
[Annales Cambriæ; Brut y Tywysogion; Asser's Vita Ælfredi; and the later and less trustworthy Gwentian Brut (Cambrian Archæological Association).]