The Celtic peoples of Ireland, and later Scotland, were an aural society. While the Romans had introduced writing to Britain, their influence did not reach Ireland and most of the social changes that came with the Romans never made it to Ireland nor Celtic society.
This lack of formal record keeping makes it difficult to develop an authoritative analysis of family genealogy. Whatever records have survived are usually written several centuries after the event and frequently - especially for Royal blood lines - are subject to fanciful associations in an attempt to legitimise the ancestory of individuals. This was particularly the case to the Book of the Four Master whose explicit goal was to establish a geneaology for the Irish Kings back to Noah.
Until written records were maintained contemporaneously with the events they describe, the authority is extremely weak. Nonetheless sufficient agreement across multiple historical roots can give us some measure of confidence in some of the facts.
A central figure in irish history is Niall, the first High King of Ireland sometimes known as Niall of the Nine Hostages suggesting there were 9 distinct tribes offering tribute to him as their king. There are various thoughts on who the tribes might have been:
However, it is Dalriada that interests us.
One of the early kings of Dalriada was Fergus son of Erc; Erc was himself the son of one of Niall’s brother thereby making Fergus a nephew of Niall. Fergus is the key figure in our story since it is his name that has been passed down the centuries as the name of the clan.
While there is general agreement that these people do indeed correspond to historical people; fixing an actual date to their lives is more difficult. Niall is reckoned to have lived during the 8th century BCE, contemporeaneous to the establishment of the Holy Roman Empire by Charlemagne.
At this time, Scotland was an unstable situation:
It was the Britons who were caught in the middle of these power struggles. While the Vikings, irish and Picts tended to use the Britons as a buffer zone againts the expanding Danelaw so they could try and sort out their own business.
However, the status quo could not be maintained: the Danelaw was gaining the upper hand against the Britons and as a consequence they were becoming a threat to the other 3.
It was the Pict Roderick who attempted bring the Celts and Viking to make peace amongst each other. A tall order as the Picts were the least of the three and did not have the resources of Ireland or Norway to bolster their advances.
First Roderick made peace with the Celts, defining a border and processes between the two factions. The Vikings eventually followed and in the face of the burgeoning threat of the Danelaw, he brought the three together against their common enemy. The vehicle was to establish a single king to lead them all
The alliance was too loose yet to be fully described as the unification of the tribe to create a Scottish nation. It would come later - provided the Danelaw could be dealt with. With some expertise, Roderick manipulated events so that:
United in circumstance, the three tribes along with the Britons managed to halt the expansion of the Danes forcing them back beyond Hadirans Wall. A degree of stability could be maintained although the Kingdom of The Rock bore the full consequences of these changes with the result that the irish Celts took effective control of the region or the two tribes merged as one although the irish tended to dominate.
While the border areas remained untamed territory as no-mans-land between Mercia and the fledgling Scottish kingdom; the Celts continued their expansion taking control of most of the Western coastal region from Dumfires and Galloway through Argyll and into the Inner and Outer Hebrides. Caithness and the northern islands remained outposts of the Norwegian king while the Picts consolidated their control of the Highlands and eastern territories maintaining the buffer zone with Northumbria.