Óengus Gaíbúaibthech

The Expulsion of the Déisi is a medieval Irish narrative of the Cycles of the Kings. It dates approximately to the 8th century, but survives only in manuscripts of a much later date. It describes the fictional history of the Déisi, a group that had gained political power in parts of Ireland during the Early Middle Ages. Part of the text's purpose is to provide the kings of the Déisi – historically the descendants of unlanded vassals to other tribes – with a mythical noble origin as the heirs to a dynasty expelled from Tara.

The story survives in two different Old Irish versions, which contain essentially the same narrative supplemented by singular additions, including tangential episodes, lists of names, and poetry. After violently recovering his niece from the depredations of the king's son of Tara, Óengus Gaíbúaibthech and his followers are dispossessed by the king and sent to wander Ireland. They tarry in Leinster for a period, but are eventually expelled from that kingdom as well. When military prowess fails them, they are able to forge a home for themselves through cunning and magic in Munster against the Osraige. As with much early Irish literature, the digressive onomastic and genealogical material is of great value. In particular, one passage describes a Déisi branch settling in Britain and founding the Kingdom of Dyfed, a matter of some interest in the context of early Irish migrations to Britain.

The story survives in an earlier and a later version, which Kuno Meyer dubbed "A" and "B". The A version dates to the 8th century, but exists only in manuscripts of a significantly later date. It survives complete in Laud MS 610 and Rawlinson MS 502, and in fragmentary form in the Book of Uí Maine and the Liber Flavus Fergusiorum. Of the complete copies, Meyer notes that the Rawlinson text contains fewer errors, but that Laud preserves more archaic spelling. The B version survives in some form in three manuscripts. The oldest of these is a fragment contained in the Book of the Dun Cow; this copy is complemented by the later two, found in H. 3. 17 and H. 2. 5, allowing for reconstruction of the text. The H. 2. 5 copy further contains several poems absent from the other manuscripts.

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