In the medieval Welsh romance of Peredur son of Efrawg, one of the tales gathered into the Mabinogion, the hero's true enemies are at last revealed to be the Gwiddonod Caerloyw — the Nine Witches of Caer Lloyw, the 'Castle of Glow' or Shining Fortress later identified with Gloucester. Far from helpless hags, they are fearsome mistresses of warfare and magic who ravage kingdoms and whose deeds have laid waste the land of Peredur's own kinsmen.
The story
The witches first take Peredur in, training him in arms and horsemanship over three weeks before he rides on. Only later does he learn that the severed head borne bleeding through his uncle's hall belonged to a cousin the Nine Witches had slain. In a story that elsewhere shadows the Grail quest, Peredur's task becomes not the finding of a sacred vessel but the destroying of the witches who plague Britain, and with Arthur and his men he returns to put them to the sword.
The episode seems to reach back into an older stratum of Celtic narrative, in which troops of nine supernatural women — echoed in the nine maidens of Avalon and the nine sorceresses of Geoffrey of Monmouth — guard, teach and destroy. Their fixing to Gloucester gives this archaic motif a local habitation, and they survive in the county's storytelling, retold in collections such as Anthony Nanson's Gloucestershire Folk Tales.