The Three Powerful Swineherds of the Island of Britain

• Drystan son of Tallwch, who guarded the swine of March son of Meirchiawn, while the swineherd went to ask Essyllt to come to a meeting with him. And Arthur was seeking (to obtain) one pig from among them, either by deceit or by force, but he did not get it;
• and Pryderi son of Pwyll, Lord of Annwfn, who guarded the swine of Pendaran Dyfed in Glyn Cuch in Emlyn;
• and Coll son of Collfrewy, who guarded Henwen, the sow of Dallwyr Dallben, when about to bring forth her litter, went to Penrhyn Awstin in Cornwall, and from there she went into the sea. And at Aber Tarogi in Gwent Is Coed she came to land.

  And Coll son of Collfrewy with his hand on her bristles wherever she went, whether by sea or by land. And in Gwent she brought forth a grain of wheat and a bee; and therefore that place is the best for wheat and bees. And from there she went to Llonion in Pembroke, and there she brought forth a grain of barley and a bee. From thence she made for the Hill of Cyferthwch in Eryri; there she brought forth a wolf-cub and a young eagle. And Coll son of Collfrewy gave the eagle to Brennach the Irishman of the North, and the wolf he gave to Menwaedd son of Arllechwedd; and these were the Wolf of Menwaedd and the Eagle of Brennach. And from thence she went to the Black Stone in Llanfair in Arfon, and there she brought forth a kitten; and Coll son of Collfrewy threw that kitten into Menai. And she was afterwards Palug's Cat.

Drystan or Drysdan is the same Sir Tristram or Tristan of romance, who was a historical Pictish prince; March is then King Mark, and Essyllt is Isolde. Arthur's attempted deceit is reminicent of Gwydion's same actions towards Pryderi.

Pryderi ap Pwyll is the subject of the Four Brances of the Mabinogi, the first four stories of the Mabinogion, equivalent to the figure of Mabon ap Modron; his father became Lord of the Otherworld for one year, and was the one to introduce swine to Britain. He was forbidden to give the swine away, and was tricked out of them by Gwydion, who was greedy. When Pryderi realized what had happened, he challened Gwydion to a duel; Gwydion killed him using magic.

Coll ap Collfrewy's tale is given above. What's worth noting is that Henwen (or Hen Wen), is the animal form of Cerridwen, goddess of poetic inspiration and keeper of a magic cauldron.

To be a swineherd is actually to be a magician, which Coll is called in other triads. Swine were an otherworldly creature, a gift of the gods, and it is thought that "swineherd" or "pig-keeper" was a way of saying "magician" or druid. This is conjecture, though if one reads Branwen uerch Llyr, it is to his swineherds that Matholwch goes for advice.