sentences:  There may also have been sixth-century kingdoms in Rhos, Meirionydd and Dunoding, all associated with Gwynedd.The name of Powys is not certainly used before the ninth century, but its earlier existence (perhaps under a different name) is reasonably inferred by the fact that Selyf ap Cynan (d. 616) and his grandfather are in the Harleian genealogies as the family of the known later kings of Powys, and Selyf's father Cynan ap Brochwel appears in poems attributed to Taliesen, where he is described as leading successful raids throughout Wales.Seventh-century Pengwern is associated with the later Powys through the poems of "Canu Heledd", which name sites from Shropshire to Dogfeiling to Newtown in lamenting the demise of Pengwern's king Cynddylan; but the poem's geography probably reflects the time of its composition, around the ninth or tenth century rather that Cynddylan's own time.