From no later than the second half of the sixth century the Uí Néill, the descendants of Níall Noígíallach,‘Níall of the Nine Hostages’, were the dominant dynasty in the northern half of Ireland. In the seventh andeighth centuries their lands extended in a broad arc from Inishowen inthe north-west to the coastland north of Dublin in the eastern midlands (see Maps 1 and 6). To judge by the admittedly imprecise procedure ofgeneration-counting, Níall, their eponymous ancestor, should haveourished in the middle of the fth century. As we shall see, there is nostrong reason to think that Nall himself ruled over anything more thanan ordinary túath. His descendants had therefore risen with astonishingspeed to the position of predominance they certainly held in thelatesixth century. Any account of their rise and, even more, any explanationof its rapidity is, however, bede villed by paucity of evidence and theuncertain value of what remains.

The very term ‘Uí Néill’ cannot be older than the sixth century, since it cannot have come into existence until the generation of Níall's grandsons, and perhaps even his great-grandsons. The most trustworthy guide to the chronology is the evidence we have in Adomnán's Life about the founder of Iona, Columba.