Historicity
The historical institution of the fian is known from references in early medieval Irish law tracts. A fian 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 fian was called a fénnid; the leader of a fian 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.
Read more about this topic: Fianna