"Pigs are not my favorite animals. Valuable and useful they are indeed, their flesh making good eating and their skins good leather. Powerful and magical they are as well, for did not Arawn King of Annwn himself give the first pigs to Pryderi, Prince of Dyfed, in token of the friendship that was between Arawn and Pryderi’s father Pwyll? And did not Gwydion the Magician steal those self-same pigs from Pryderi by a trick, and bring them home to Gwynedd? ... No, I like a nice dish of pig-meat as well as the next man, but I hold with the Irish that the pig-run should be kept out of sight and scent and sound of the owner’s house, and not only because of the smell of it."
So says my narrator Gwernin in Storyteller, and I have to say that by and large I agree with him - although for less personal reasons. Archeology indicates that many Britons, both during the Roman period and later, shared his taste for pork. It seems to have been particularly popular on Roman-era urban sites, and also at some legionary forts, although it was usually second there after beef. Pork bones also turn up with interesting frequency as offerings in graves, suggesting that it was either a prestige food or in some way connected with the supernatural. The story about Gwydion's pig raid (in the fourth branch of the Mabinogion) strengthens the supernatural connection, for Annwn was the Celtic underworld, and later in that story a sow is again involved in an equally magical context.
The Welsh Triads, a compilation of lists of people, animals, and occurences grouped in threes which served as a memory aid for bards and storytellers, has an interesting item called "Three Powerful Swineherds of the Island of Britain." The Swineherds in question were Pryderi (see above), Drystan (=Tristan) and Coll son of Collfrewy, and the Drystan part of the triad seems to refer to a lost Arthurian tale. Another Arthurian connection occurs in the tale of Culhwch and Olwen, where the hero Culhwch gets his name because he was born in a pig-run. Pigs in general have an inportant place in Celtic literature, and in Irish sources pig-meat was considered the food of the gods. They could also lead to trouble there, as in the tales of Mac Datho's Pig and Bricriu' Feast.
Think about that when you bite into your next ham sandwich.