Fenian cyclealso called Fionn cycle or Ossianic cycleIn Irish literature, tales and ballads centering on the deeds of the legendary Finn MacCumhaill (MacCool) and his war band, the Fianna Eireann. An elite volunteer corps of warriors and huntsmen, skilled in poetry, Fianna flourished under the reign of Cormac mac Airt in the 3rd century AD. Fenian lore attained its greatest popularity about 1200, when the cycle's outstanding story, Colloquy of the Old Men, The, was written down. Other earlier tales were recorded in manuscripts such as Book of the Dun Cow, The (c. 1100) and Book of Leinster, The (c. 1160). The Fenian cycle remains a vital part of Irish folklore and contains many of the best-loved folktales of the country.
An early tale, The Boyish Exploits of Finn (Macgnimartha Finn), tells how, after Cumhaill (Cool), chief of the Fianna, is killed, his posthumous son is reared secretly in a forest and earns the name Finn ("The Fair") by his exploits. He grows up to triumph over his father's slayer, Goll MacMorna, to become head of the Fianna, which later includes his son Oisin (Ossian), the poet, his grandson Oscar, the handsome Diarmaid (Dermot), and his former clan enemy Goll MacMorna.
The other tales of the cycle deal with Fianna's rise and fall. Its disintegration begins when Diarmaid elopes with Grainne (Grace), a king's daughter whom Finn, as an old man, wishes to marry. Later, when Diarmaid is wounded, Finn lets him die for lack of water. The king and people finally turn against the overbearing Fianna, a conflict that culminates in the Battle of Gabhra, in which the Fianna is destroyed. Related to the Fenian sagas is a series of tales concerning Cormac mac Airt, his grandfather Conn of the Hundred Battles, and his son Cairbre of the Liffey.