In the story The Expulsion of the Déisi, the great-great-great-grandson of legendary high king of Ireland, Fedlimid Rechtmar (AD 104, according to Ireland's mythological timeline), is Art Corb. His four sons are expelled from Tara following a failed bid to take the high kingship. Cormac mac Airt is also mentioned in the eighth century text when he is blinded by Óengus Gaíbúaibthech of the Déisi. As no high king can remain in place if he bears a physical blemish, Cormac is replaced by Eochaid Gonnat, although a year later he is killed in battle by Cormac's son, Cairbre Lifechair.
Art Corb's sons each go their own way. The group led by Eochaid Allmhuir (Allmhuir meaning 'over-sea') settles in Demetia around the start of the fourth century, while another eventually settles amongst the Déisi of southern Munster (the Déisi Muman). These events have been tied to Scotti (Irish) pirate raids along the length of Britain's western and southern coasts in the fourth and fifth centuries, and to the foundation of the Brito-Irish kingdoms of Dyfed and Brycheiniog. 1
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It would not be without reason to claim...that Dyfed (which contains the largest concentration of Welsh ogams) was settled by immigrants from Waterford and that the claim of dynastic origin stated in the Indarba was at least not impossible. However, this general statement does not bear up if the specific details of the Indarba are examined more closely. For instance,... the Historia Brittonum stated that the Irish settlers in south Wales were of the neighbouring kingdom of Uí Liatháin, which was itself not bereft of ogam inscriptions.... Furthermore, as Tomás Ó Cathasaigh has stressed, according to the Indarba the migration of Eochaid Allmuir did not depart from Waterford nor (as some earlier scholars stated) from Meath, but during the Leinster sojourn.... [For] Ó Cathasaigh, the ogam-using settlers from Waterford represent an independent migration from that of Eochaid Allmuir recounted in the Indarba. In Leinster, the text locates the Déisi in territory seized from Uí Bairrche, until they were subsequently expelled thence four generations later. There was more than one group of Uí Bairrche in early medieval Leinster; if those located on the southern coast of County Wexford were intended in the Indarba, then this would be suitable as a point of departure to Dyfed. However, such an argument would serve to undermine the otherwise important coincidence that Waterford is associated both with ogams and the Déisi and, in effect, remove that convenient piece of independent archaeological verification of the Indarba.
Another problematic 'detail' in the Indarba is the date of Eochaid Allmuir's migration. As we shall see, the place of Eochaid's migration in 'absolute' chronology has ranged over two hundred years according to different interpretations; and recently both Ó Cathasaigh and Bruce Coplestone-Crow have sought to dissociate Eochaid Allmuir from the population movement which introduced the use of ogam into south Wales, though in so doing they would reverse the relative order of the two migrations. These differences between the various interpretations of Eochaid Allmuir's migration and especially over its date are probably symptomatic of the nature of the various sources which have been employed to determine it; and it would perhaps be more useful to approach the problem from the perspective of the Indarba itself.
The total possible date-range in which differing interpretations have placed the migration of Eochaid Allmuir to Dyfed is between ca 270 and ca 500. In addition to the epigraphic evidence, the dates have been determined by the statement in the Annals of the Four Masters that Cormac mac Airt was blinded and the Déisi were expelled from Tara in A.D. 265, and also by differing attempts to 'date-guess' by generation-counting the extant Irish and Welsh versions of the Dimetian pedigree. The latter have been based on the obit of Maredudd ap Tewdws in 796 or the mid-sixth century floruit of Vortipor as contemporary of Gildas. The most persistent date for the migration of the late-third century was established by John Rhys and Kuno Meyer through a combination of the Four Master's annal and date-guessing. Taking the Four Masters' date, Meyer pointed out that calculating from ca 270 (as an estimate for the migration) with a thirty-three year biological-generation average, the intervening (fourteen) generations would give a floruit of ca 730 for Tewdwr-Tewdws ap Rhain; and this date 'is fully confirmed' by the obit of Maredudd in the Annales Cambriae.... 2
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