Déisi

The Déisi were a class of peoples in ancient and medieval Ireland. The term is Old Irish, and derives from the word déis, meaning "vassal" or "subject"; in its original sense, it designated groups who were vassals or rent-payers to a landowner.^[1] Later, it became a proper name for certain septs and their own subjects throughout Ireland.^[2] The various different peoples listed under the heading déis shared the same status in Gaelic Ireland, and had little or no actual kinship, though they were often conceived of genetically related. Déisi groups included the Déisi Muman (the Déisi of Munster), Déisi Temro (of Tara), Déisi Becc (located in the Kingdom of Mide) and the Déisi Tuisceart (the Northern Déisi; a sept of which would become famous as the Dál gCais).

The Déisi are the subjects of one of the most famous medieval Irish epic tales, The Expulsion of the Déisi.^[3] This literary work, first written sometime in the eighth century, is a pseudo-historical foundation legend for the medieval kingdom of Déisi Muman, which seeks to hide the historical reality that the kingdom's origins lay among the indigenous tributary peoples of Munster. To this end it attributes to "the Déisi" an entirely fictive royal ancestry at Tara.^[1] The term "Déisi" is used anachronistically in The Expulsion of the Déisi, since its chronologically confused narrative concerns "events" that long predate the historical development of déisi communities into distinct tribal polities or the creation of the kingdom of Déisi Muman.^[4] The epic tells the story of a sept called the Dal Fiachach Suighe, who are expelled from Tara by their kinsman, Cormac mac Airt, and forced to wander homeless. After a southward migration and many battles, part of the sept eventually settles in Munster.

At some point during this migration from Tara to Munster, one branch of the sept, led by Eochaid Allmuir mac Art Corb, sails across the sea to Britain where, it is said, his descendants later ruled in Demed, the former territory of the Demetae (modern Dyfed). The Expulsion of the Déisi is the only direct source for this "event". The historicity of this particular passage of the epic apparently receives partial confirmation from a pedigree preserved in the late tenth-century Harleian genealogies, in which the contemporary kings of Dyfed claim descent from Triphun, a great-grandson of Eochaid Allmuir, although the Harleian genealogy itself presents an entirely different version of Triphun's own ancestry in which he descends from the Roman Emperor Constantine I. This manifest fiction possibly reflects a later attempt to disguise the Irish origin of the dynasty.^[5] If the relocation of some of the "Déisi" to Dyfed is indeed historical, it is unclear whether it entailed a large-scale tribal migration or merely a dynastic transfer, or both as part of a multi-phase population movement.^[6] In any case, scholarship has demonstrated that it cannot have taken place as early as the date implied in the The Expulsion of the Déisi (i.e. shortly after the blinding of Cormac mac Airt, traditionally dated AD 265), but must have occurred in the second half of the fourth century at the earliest, and possibly dates to the sub-Roman period in the early fifth century.^[7] In this period other southern Munster dynasties were also active in raiding and settling western Britain, most prominently the Uí Liatháin, a long-established and more powerful dynasty, whose territory in Munster lay to the west of the region in which the kingdom of Déisi Muman later emerged.

The term déisi is also virtually interchangeable with another Old Irish term, aithechthúatha (meaning "rent-paying tribes", "vassal communities" or "tributary peoples"). From the eighteenth century it had been suggested that this term might be the origin of the Attacotti who are reported attacking Roman Britain in the 360s, although the argument has been doubted on etymological grounds. This argument has recently been reopened, however, by a proposed equation of déisi – aithechthúatha – Attacotti in a late fourth-century context.^[8]

• County Waterford
• Bruff
• Kings of the Déisi Muman
• Dāsa - a group identified as the enemies of the Aryan tribes in the Rigveda.

• Irish kings
• Medieval Gaels
• Ancient peoples
• Ancient Ireland

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