>>3606177We can't be certain when the Picts arrived in Ireland, although it's certain they came there from Britain. The Irish (Scotti) identified them as such.
However, it seems likely that the Roman incursions into northern Britain from the 1st century onward would have produced refugees, particularly from the contested lands between the Antonine Wall and Hadrian's Wall. Those lands were occasionally garrisoned and were otherwise inhabited by the Romanised Damnoni and Votadini.
The Scotti raided them frequently. St. Patrick, a Damnoni, was kidnapped from his home near Dumbarton and brought to Ireland.
When Rome pulled out of Britain completely, Coel Hen became the most powerful man in the region. Briefly.
Fergus Mor and the Dal Riata invaded, united with the Picts, and killed Coel Hen and his army almost to a man.
It's now more or less accepted that the Dal Riata of Antrim were, like the Anglecynn, a hybrid people - part Scot, part (maybe even majority) Pictish.
While that much is true, the rest is speculation. However, it does appear that these people were reclaiming lands lost to Rome and granted to compliant Romano British tribes.
Anecdotally, incidence of red-hair in Ireland is concentrate in the north. Together with northern Scotland, these are the highest concentrations in the world.
Of course, Gaels and Britons have common ancestry in any case, but it is very likely that the reason we can't determine Pictish ancestry is that it is almost identical to that of the Scotti/Riata. (It's impossible to distinguish between most people from Antrim and parts of Scotland, genetically speaking).
