Battle of Arfderydd - Wikipedia
A possible site for the Battle of Arfderydd. Between the King of Strathclyde, Rhydderch Hael, and the King of South West Scotland Gwenddoleu ap Ceidio. Gwenddoleu's bard was Myrddin (Merlin, yes that Merlin).
https://en.wikipedia.org/wiki/Battle_of_ArfderyddOpen linkView original on lemmy.world
Side note: "Myrddin's grave is reputed to lie near the River Tweed in the village of Drumelzier near Peebles, although nothing remains above ground level at the site."