Wikipedia
Utagaki
Utagaki (歌垣), also read kagai (嬥歌), was an ancient Japanese ritual peasant gathering. Villagers would sing and dance on the way up to a mountaintop, where singing, dancing, eating, and the reciting of poetry would occur, in celebration of the beginning of spring or autumn. Closely associated with harvest rites, and therefore fertility, these events often also led into much free sexual activity.
Originating prior to the Nara period, the practice of utagaki reached its height during that period (710-794). Many of the songs and poems, as well as accounts of the ritual itself, are recorded in the Man'yōshū and other contemporary documents, making them among the oldest forms of literature in Japan.