In which I ponder whether Sueno's Stone commemorates a victory of Constantín II of Alba over the Vikings in 904 AD.
A bit late to this (brought back by your wonderful Auldearn post) but surely one argument for a northern location is simply that the Annals of Ulster record it as a victory for the men of Fortriu ("la firu Fortrenn" - AU 904.4)?
Assuming the identification of Fortriu with the north is correct, and assuming the narrative of a shift in the centre of power to south of the mounth post-839 is also correct, it seems inherently unlikely that it would be the army of the (weaker) north that was defending the (stronger) south against vikings deep within southern territory in Strathearn in 904? Woolf argues against 904 being used as evidence for Fortriu being equated with Strathearn on the basis that "It could have been an away match", but in fact it would have been an away match for both sides - the Vikings and the men of Fortriu fighting each other within the heartland of southern Alba. A northern location of the battle, with the men of Fortriu defeating the Vikings while defending their own heartland in the hinterland of Forres does seem on the face of it more likely.
An alternative (or possibly complementary) interpretation of the AU description might be that the post-839 power dynamic between north and south was a bit more complicated. As you touched on in your earlier post of Forres, Woolf ("Pictland to Alba", pp223-224) and McGuigan ("Mael Coluim II", pp51-55) both suggest this, but come to diametrically opposite conclusions from the same evidence - that no descendants of Causantin mac Cinaeda died south of the Mearns, while only one descendant of Aed mac Cinaeda didn't. McGuigan argues that this shows that Forres was part of Clann Causantin's home territory, and that they were thus based in the north; while Woolf argues that it shows that Clann Causantin was based in the south, with Clann Aeda being based in the north, as the demise of Clann Aeda coincides with the rise of the Moray-based Clann Ruadri in their place.
If it is Woolf's conclusion that is correct, then Causantín mac Aeda's powerbase would have been in the north, which might explain why it was specifically the men of Fortriu fighting the Vikings in 904, wherever the battle took place. This might also explain the line immediately before the section you quoted from the Fragmentary Annals of Ireland, which seems to directly equate the "men of Fortriu" with the "men of Alba" later in Causantín's reign in 918: "?918 Almost at the same time the men of Foirtriu and the Norwegians fought a battle. The men of Alba fought this battle steadfastly, moreover, because Colum Cille was assisting them".
But then, if Causantín mac Aeda's power was centred in the north, doesn't that itself make a northern location for 904 more likely?
Excellent as always. Assuming the southern Stathearn this also fits with earlier raiding like the battle of dollar. The Roman road of course ran along strath Allan and strath earn and would be the obvious route for raiders from the coast trying their luck? Might the victory be explained by being caught too far from safety along the road. Lots of supposition of course!