Dyrnwyn, the flaming sword, lost for centuries beneath the earth.
A hamper that feeds a hundred, a knife to serve twenty-four,
A chariot to carry a man on the wind,
A halter to tame any horse he might wish.
The cauldron of the Giant to test the brave,
A whetstone for deadly sharpened swords,
An entertaining chess set,
A crock and a dish, each to fill one’s every wish,
A cup that bestows immortality on those worthy of it,
And the mantle of Arthur.
His healing sword descends;
Our enemies flee our unseen and mighty champion.
–Taliesin, The Thirteen Treasures, The Black Book of Gwynedd
When JK Rowling talks about the deathly hallows in the Harry Potter books, she is giving a nod to the Thirteen Treasures, which she didn’t make up, in that their roots lie in the mythology of Britain dating back to the Celts. In the Deathly Hallows, the treasures are an invisibility cloak, a stone that brings the spirit of someone back from the death (for a time), and a powerful wand.
The original thirteen treasures are tied to the Arthurian legend. In some sources, Merlin seeks them, in others, Arthur or his men are sent on quests to retrieve them.
“The “Thirteen Treasures of Britain” were famous in early legend. They belonged to gods and heroes, and were current in our island till the end of the divine age, when Merlin, fading out of the world, took them with him into his airy tomb, never to be seen by mortal eyes again. According to tradition, they consisted of a sword, a basket, a drinking-horn, a chariot, a halter, a knife, a cauldron, a whetstone, a garment, a pan, a platter, a chess board, and a mantle, all possessed of [marvelous qualities] . . .
It is these same legendary treasures that reappear, no doubt, in the story of “Kulhwch and Olwen”. The number tallies, for there are thirteen of them . . . That there should be discrepancies need cause no surprise, for it is not unlikely that there were several different versions of their legend. Everyone had heard of the Thirteen Treasures of Britain. Many, no doubt, disputed as to what they were. Others might ask whence they came. The story of “Kulhwch and Olwen” was composed to tell them. They were won by Arthur and his mighty men.” http://www.sacred-texts.com/neu/celt/cml/cml26.htm
From Wikipedia: “The Thirteen Treasures of the Island of Britain (Welsh: Tri Thlws ar Ddeg Ynys Prydain) are a series of items in late medieval Welsh tradition. Lists of the items appear in texts dating to the 15th and 16th centuries. Most of the items are placed in the Hen Ogledd or “Old North”, the Brythonic-speaking parts of what is now southern Scotland and Northern England; some early manuscripts refer to the whole list specifically as treasures “that were in the North”. The number of treasures is always given as thirteen, but some later versions list different items, replacing or combining entries to maintain the number. Later versions also supplement the plain list with explanatory comments about each treasure.” http://en.wikipedia.org/wiki/Thirteen_Treasures_of_the_Island_of_Britain
Wikipedia has a list (see link above), and another can be found here: http://www.tartanplace.com/faery/thirteen.html
and here you can take a quiz about them!: http://www.ancientworlds.net/aw/Post/1089305