Culhwch ac Olwen is the oldest Arthurian story we have. It survives in the White Book of Rhydderch and the Red Book of Hergest, the same medieval Welsh manuscripts that give us the Mabinogi, and it is older than anything Chrétien de Troyes ever wrote in France. The Arthur in this story is not the courtly king of later romance — he is a Welsh warlord with a war-band, a magical ship, and a list of impossible favours owed to his cousin.
The cousin is Culhwch, and he is under a curse. His stepmother has sworn that he will never marry any woman but Olwen, daughter of the giant Ysbaddaden Bencawr — Ysbaddaden Chief Giant. The trouble is that Ysbaddaden is fated to die the day his daughter takes a husband, and so he keeps her locked away in a fortress no suitor has ever entered alive.
Culhwch rides to Arthur's court at Celliwig in Cornwall and asks his cousin for help. Arthur agrees, and what follows is one of the great list-tales of European literature. Arthur's warriors are named in a rolling, hypnotic catalogue — Cei, Bedwyr, Gwalchmei, dozens more — and the band sets out to find Olwen.
When they meet her, the description has never been bettered: 'More yellow was her head than the flower of the broom, and her skin was whiter than the foam of the wave, and fairer were her hands and her fingers than the blossoms of the wood-anemone amidst the spray of the meadow fountain. And four white trefoils sprang up wherever she trod. And therefore was she called Olwen' — Ol-wen, White Track.
Ysbaddaden agrees to the marriage on one condition: that Culhwch perform forty impossible tasks, the anoethau. Hunt the great boar Twrch Trwyth and take the comb and shears from between his ears. Win the sword of Wrnach the Giant. Find Mabon son of Modron, who has been imprisoned since he was three nights old. Recover the cauldron of Diwrnach the Irishman. On and on it goes — each task a tale in itself, each one drawing in more of Arthur's war-band.
They do it all. Twrch Trwyth is hunted from Ireland across Pembrokeshire and into the Severn Sea. Mabon is found chained in a Gloucester prison. Ysbaddaden is shaved with the boar's comb — the shave that ends his life — and Olwen marries Culhwch at last. The wedding is the death of her father, exactly as the prophecy said.
Wear Culhwch and Olwen and you wear the deepest Welsh root of the whole Arthurian tradition — the white flowers in the grass, the long list of names, and the oldest love-story we have written down in this language.