The Mabinogion

The Mabinogion are the earliest prose literature of Britain. The stories were compiled in the 12th-13th centuries from earlier oral traditions by medieval Welsh authors. The two main source manuscripts were created c. 1350-1410, as well as some earlier fragments. But beyond their origins, first and foremost these are fine quality storytelling, offering high drama, philosophy, romance, tragedy, fantasy, sensitivity, and humour; refined through long development by skilled performers.

(Source: Wikipedia)