The Déisi were a social class in Ireland between the ancient and early medieval period. The various peoples listed under the heading déis shared a similar status in Gaelic Ireland, and had little or no actual kinship, though they were often thought of as genetically related. During the era of Roman rule in Britain, many members of the Déisi were recorded as settling in western coastal areas (especially the areas known later as Wales, Cornwall and Devon).
During the early Middle Ages some Déisi groups and subgroups exerted great political influence in various parts of Ireland. For instance, in Munster, a subgroup of Déisi constituted a regional kingdom, Déisi Muman, and were part of the hegemony of the Eoganachta confederacy.
Etymology
Déisi is an Old Irish term that is derived from the word déis, which meant in its original sense a "vassal" or "subject", a designated group of people who were rent-payers to a landowner. Later, it became a proper noun for certain septs and their own subjects throughout Ireland.
History and contexts
The early histories of the Déisi groups are obscure. As a class that evolved from peoples tied by social status rather than kinship, groups had largely independent histories in different parts of Ireland. While some medieval texts attempt to give the Déisi an aristocratic origin, these are later fabrications dating to the period after the Déisi had gained political power. Despite their tributary origins, representatives of at least one Déisi population would eventually achieve spectacular success, founding a powerful medieval dynasty which is still in existence.
Déisi groups included the Déisi Muman (the Déisi of Munster), Déisi Temro (Déisi of Tara), Déisi Becc ("Little Déisi," located in the Kingdom of Mide) and the Déisi Tuisceart (the Northern Déisi; a sept of which would become famous as the Dál gCais).
Today, 'Déisi' is an informal term for County Waterford and its people.
Déisi Muman
The Déisi Muman were a prominent enough power to form their own regional kingdom in Munster from a fairly early date. In a recent title, Paul MacCotter states "The regional kingdom of Déisi Muman must have existed in roughly its present location from a very early period. Oghams dating perhaps from the fifth century record unique first names associated with its kings." According to Francis John Byrne, there are certain inscriptional hints that both the Eóganachta and their Waterford Déisi vassals may have been of fairly recent Gaulish origins. The ancestors of the Eóganachta are known as the Deirgtine and they are also believed to have been active in Roman Britain, one piece of evidence being the name of their capital Cashel, thought to be inspired by the Roman castella they observed on raids. The Déisi Muman enjoyed a position in the later Eóganachta overkingdom suggesting of a special relationship. Byrne mentions it was noticed by Eoin MacNeill that a number of the early names in the Eóganachta pedigrees are found in oghams in the Déisi country of Waterford, among them Nia Segamain (NETASEGAMONAS), after the Gaulish war god Segomo. According to MacNeill, the Waterford Déisi and the Eóganachta at Cashel "cannot well be disconnected".
The Uí Liatháin dynasty were western neighbors of the proto-Déisi Muman along the southern Irish coast and raided and colonized parts of Wales and Cornwall. They are the best characterized of the South Irish colonists because of clear references to them by name in both early Irish and early British sources, while a presence of the Déisi Muman cannot actually be confirmed. Also noted are the Laigin, particularly in North Wales.
Possible presence in Britain
The Déisi Muman are the subjects of one of the most famous medieval Irish epic tales, The Expulsion of the Déisi. 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. 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. 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.