Síle Ní Mhurchú at the Dublin Review of Books:
The earliest reference we have to Fionn mac Cumhaill is a brief one in a poem by Senchán Torpéist which may date back as far as the seventh century, and in which he is depicted as belonging to an evil band of men who cause warlike brandishing from ships, a negative portrayal which may seem surprising to those more familiar with the later stages of the Cycle. Fionn’s Fianna are based on the historical institution of the fían that provided an outlet for the energies of young free-born men who had not yet come into their inheritances, allowing them to form bonds with people outside their own kinship groups and improve their hunting and fighting skills; the early law texts suggest that fíana also performed a role in maintaining law and order. They were, however, seen by the church as a disruptive force given to robbery and plundering, which would explain why such groups are vilified in early writings; it was only after the fían as an institution had disintegrated that a more accepting attitude towards fictional fíana could be permitted.
Other fían-leaders besides Fionn feature in early Irish literature and thus Murray devotes a chapter to the best-documented of these, Fothad Canainne, demonstrating that he was the star of his own literary cycle, of which only fragments now remain, before being subsumed into the Finn cycle. There was also a regional component to the cultivation of the early Finn Cycle, one example being three interlinked tales probably of the eighth century and set around the river Suir near Cathair Dhún Iascaigh (modern-day Cahir, Co Tipperary) – Bruiden Átha Í (The Contention of Áth Í), Marbad Cúlduib (The Slaying of Cúldub) and the tale now known as “Finn and the Man in the Tree”.