The Worm Ouroboros

The Worm Ouroboros is a heroic high fantasy novel by English writer E.R. Eddison. First published in 1922, the book describes the long war between King Gorice of Witchland and the Lords of Demonland. 
It is set in an imaginary world that appears medieval and reminiscent of Norse sagas. The work is slightly related to Eddison's later Zimiamvian Trilogy, and collectively they are sometimes called the Zimiamvian series.
The book was illustrated by Keith Henderson, who also illustrated books by Geoffrey Chaucer and W.H. Hudson.
The work is described as fantasy because it is not an attempt to imagine the future (as does much science fiction) but instead presents an imagined world, rather as does "The Lord of the Rings".