In reply to Steve Parker:
From the annals of Ireland:
158 AD - After the 35 year reign of Conn of the Hundred Battles, this was the first year of Conaire, son of Modh Lamha, in sovereignty over Ireland. Conaire was also a son-in-law of Conn.
165 AD - Conaire, son of Mogh Lamha, after having been eight years in the sovereignty of Ireland, fell by Neimhidh, son of Sruibhgheann. This Conaire had three sons, Cairbre Musc, from whom the Muscraighe are called; Cairbre Baschaein, from whom are the Baiscnigh, in Corca Baiscinn; and Cairbre Riadal, from whom are the Dal Riada. Saraid, daughter of Conn of the Hundred Battles, was the mother of these sons of Conaire, son of Modh Lamha.
[Cairbre Riadal, following a famine in the South, led his people to the extreme Northeast of Ireland, and some of them across to the nearest part of Scotland, where they settled, forming the first important colony of Scots (Irish) in Alba.]
Q: The fist establishment of Dal Riada?
195 AD - After Art, the son of Conn of the Hundred Battles, had been thirty years in the sovereignty of Ireland, he fell in the battle of Magh Mucruimhe, by Maccon and his foreigners. In the same battle, along with Art, fell also... and ****Beinne Brit, King of Britain****, was he who laid violent hands upon them. Beinne was slain by Lughaidh Lagha, in revenge of his relatives. Lioghairne of the Long Cheeks, son of Aenghus Balbh, son of Eochaidh Finn Fuathairt, was he who laid violent hands upon Art in this battle of Magh Mucruimhe, after he had joined the forces of Maccon.
Q: It's worth noting that the Fuathairts hung out around Wexford, reckoned to be a stronghold of the Brigantes. If the King of Britain and his 'foreigners' along with local cruithne (Brythonic - Pict) Fuathairts were scrapping with the Gaels in 195 AD and winning battles does this show a level of cross sea activity the Romans couldn't compete with?
240 AD - The battle of Magh Techt, and the fleet of Cormac sailed across Magh Rein (i.e. across the sea), this year, so that it was on that occasion he obtained the sovereignty of Alba Scotland.
Q: A Dal Riada takeover?
663 AD - Cearnach Sotal, son of Diarmaid, son of Aedh Slaine, died, together with the aforesaid persons, of a mortality which arose in Ireland, on the Calends of the August of this year, in Magh Itha, in Fotharta.
Q: Could this be the same plague which wiped out half the population of southern Britain in the mid C7th which allowed the Saxons to overrun the harvest bowl of England. There is a large influx of refugee Brits into Brittany following this event.