Prose
The word "prose" first appears in English in the 14th century. It is derived from the Old French "prose", which in turn originates in the Latin expression "prosa oratio" (literally, straightforward or direct speech).
Medieval literature
Prose tales first emerged in Britain: the intricate "Mabinogi" quartet about princely families, notably anti-war in theme, and the romantic adventure "Culhwch and Olwen", famous for the earliest mention of King Arthur. (The "Mabinogi" is not the same as the "Mabinogion", a collection of disconnected prose tales, which does, however, include both the "Mabinogi" and "Culhwch and Olwen".) These works were compiled from earlier oral tradition c. 1100.