Baelrath
editA ring, called the Warstone, created by the female war goddesses, Macha & Nemain, in the Fionavar.
Source:
Part II : Rachel's Song Book: The Summer Tree of the Fionavar Tapestry by Guy Gavriel Kay
"The Baelrath it was named, long ago, the Warstone. It is of the wild magic," the Seer said, " a thing not made by man, and it cannot be controlled like the shapings of Ginserat or Amairgen, or even the Priestesses. It has been lost for a very long time, which has happened before. It is never found without reason, or so the old tales say."