The Ainu had no writing system of their own, and much of Ainu mythology was passed down as oral history in the form of kamuy yukar (deity epics), long verses traditionally recounted by singers at a gathering. Each kamuy yukar recounts a deity's or hero's adventures, usually in the first person, and some of them are of great length, containing as many as 7,000 verses.[2] Some yukar contradict each other, assigning the same events to different deities or heroes; this is primarily a result of the Ainu culture's organization into small, relatively isolated groups.[3] Records of these poems began to be kept only in the late 19th century, by Western missionaries and Japanese ethnographers; however, the Ainu tradition of memorizing the yukar preserved many.