In a Welsh poem, Cei (Kay) is said to have “pierced nine witches” in the “uplands of Ystafngwn”. The theme of nine enchantresses is recurring in Welsh legend.

In the story of Peredur, Peredur kills the nine Hags of Gloucester to avenge a cousin’s murder. In The Spoils of Annwn, we learn that a magic cauldron seized by Arthur from the Otherworld was

gently warmed by the breath of nine maidens.

In Geoffrey of Monmouth’s Vita Merlini – influenced heavily by Welsh legend – Arthur is taken to the Island of Apples (Avalon), ruled by nine sorceresses, including Morgan le Fay. The theme seems to have origins in classical mythology.

In the first century, Roman geographer Pomponius Mela described and island off the coast of Brittany inhabited by nine enchantresses with the power to heal the sick.

See also
Nine Sisters | The Legend of King Arthur
Nine Worthies | The Legend of King Arthur
Ystafngwn | The Legend of King Arthur

Sources
Preiddeu Annwfn | Attributed to Taliesin, c. 900
Pa gur yv y porthaur | Poem 31 of the Black Book of Carmarthen, probably c. 1100
Vita Merlini | Geoffrey of Monmouth, c. 1150
Peredur | 13th century