The term "Edda" (; Old Norse Edda, plural Eddur) applies to the Old Norse Prose Edda and has been adapted to fit the collection of poems known as the Poetic Edda which lacks an original title. Both works were written down in Iceland during the 13th century in Icelandic, although they contain material from earlier traditional sources, reaching into the Viking Age. The books are the main sources of medieval skaldic tradition in Iceland and Norse mythology.