Mabinogion

First published in 1848. According to Wikipedia: "The Mabinogion is the title given to a collection of eleven prose stories collated from medieval Welsh manuscripts. The tales draw on pre-Christian Celtic mythology, international folktale motifs, and early medieval historical traditions. While some details may hark back to older Iron Age traditions, each of these tales is the product of a highly developed medieval Welsh narrative tradition, both oral and written. Lady Charlotte Guest in the mid 19th century was the first to publish English translations of the collection, popularising the name "Mabinogion" at the same time.”