The Câd Goddeu, or Battle of the Trees, is an early Welsh poetic cycle penned by Gwydion ap Gwyn. The poem, written in a mix of heroic couplets and tetrameter, tells in a riddling and obtuse way of a war between the alder and the ash, with the other trees allied on either side. Robert Graves, in his controversial novel The White Goddess, postulates that the alder stands for Bran or Vran, the Welsh name for the Judeo-Christian God, while the ash stands for Odin or Woden, the Norse god of thunder. Since both gods were associated mythographically with the raven, it makes sense that they should be fighting for dominance.
As a record of the struggle between Judeo-Christian belief and old-world Norse mythology, the Câd Goddeu stands in the company of such classic poetic works as Beowulf and the Norsk Eddas. However, the Câd Goddeu predates Beowulf by a good three centuries; it is not written in the stilted Early English language of the bards, but in the far older Welsh, or Cymric, dialect of the Pictish invaders who came to England in the sixth and seventh centuries, and which Graves describes as remnants of the pan-European Sea Peoples.
In modern times, it has been suggested that J.R.R. Tolkien, in the The Lord of the Rings, may have based some of his "Ents" on the characters of the Câd Goddeu. Certainly the name "Treebeard" recalls one of the nicknames of Odin (Woden), and Tolkien is known to have pulled much of his source material from the Red Book of Westmarch, or Hergest, in which the Câd Goddeu is reprinted.