Fianna
Fianna (singular fiann) were small, semi-independent warrior bands in Irish mythology and Scottish mythology. They are featured in the stories of the Fenian Cycle, where they are led by Fionn mac Cumhaill.
They are based on historical bands of landless young men in early medieval Ireland known as kerns.
Historicity
The historical institution of the fiann is known from references in early medieval Irish law tracts. A fiann was made up of landless young men and women, often young aristocrats who had not yet come into their inheritance of land. A member of a fiann was called a fénnid; the leader of a fiann was a rígfénnid (literally "king-fénnid).
Geoffrey Keating, in his 17th-century History of Ireland, says that during the winter the fianna were quartered and fed by the nobility, during which time they would keep order on their behalf, but during the summer, from Beltaine to Samhain, they were obliged to live by hunting for food and for pelts to sell. Keating's History is more a compilation of traditions than a reliable history, but in this case scholars point to references in early Irish poetry and the existence of a closed hunting season for deer and wild boar between Samhain and Beltaine in medieval Scotland as corroboration.