Irish title of a 12th-century narrative of the Cycle of Kings known in English as The Frenzy of Suibne, The Madness of Sweeney, etc. It is the third and best known of a trilogy about a 7th-century Ulster petty king, Suibne Geilt [Ir., mad Suibne or Sweeney], who lost his reason at the Battle of Mag Rath (or Moira) in 637. The first story, Fled Dúin na nGéd [The Feast of Dún na nGéd], deals with events before the battle, which itself is described in the second story, Cath Maige Rátha [The Battle of Mag Rath]. Many modern readers have found Suibne's wanderings across Ireland, from treetop to treetop, among the most affecting in early Irish literature. Although Suibne first resists and later accepts Christianity, his story contains many elements of pre-Christian mystery.
Suibne son of Colmán is a king of Dál-nAraide in the former (until 1974) counties Antrim and Down of eastern Northern Ireland. He seeks to expel the evangelizing St Rónán from his kingdom, but his wife Eórann dissuades him. Angry at the sound of Rónán's bell, Suibne rushes from his castle, but Eórann grabs his cloak so that he goes through the door naked. The pagan king throws Rónán's psalter into a lake and is about to do violence to the saint when he is called to the Battle of Mag Rath. Rónán gives thanks to God for being spared but curses the king, asking that he may wander through the world naked, as he has come naked into his presence.
Rónán tries to make peace between the contending armies at Mag Rath without success. When he tries to bless the warriors, including Suibne, the king throws his spear at the saint; a second spear breaks against Rónán's bell, its shaft flying in the air. Rónán curses Suibne a second time, wishing that he may fly through the air like the shaft of his spear and that he may die of a cast spear. When Suibne tries to rejoin the battle he is seized with trembling and flees in frenzy like a wild bird. His feet barely touch the ground, and land at last on a yew tree. After Suibne's withdrawal, his opponents are victorious. When a kinsman is unable to bring Suibne back among his people, the mad king flies to different parts of Ireland, settling for long intervals in the glen of madmen known as Glenn Bolcáin.
His one faithful friend during this torment is Loingsechán, who may be a uterine brother or a foster-brother. Loingsechán rescues Suibne three times and keeps him informed about his family. Eórann, who has gone to live with Guaire, remains faithful to Suibne, even though he visits her and tells her she would be better off without him. On several occasions Suibne regains his reason, and once he seeks to return to his people, but Rónán prays that the king should not be allowed to come back and resume his persecution of the Church. The narrative is interspersed with a number of poems, some of them in Suibne's voice. Two of the most memorable, coming late in the narrative, are in praise of nature and of trees.