The site of a battle, probably historical, fought between warring British clans. Scholars have plausibly identified it with Arthuret (no connection to Arthur), eight miles north of Carlisle, in Liddesdale. The Annales Cambriae say that the battle occurred in 573, and the Triads call it "futile", saying that it began over a lark’s nest, referring to the Fort of the Lark on the edge of Solway Firth. The fact that the battle was for a 'lark's nest' appears to indicate that the fight was actually for ownership of the important harbour of Caerlaverlock, which translates as Fort Lark.
At the battle, the warlord Gwenddolau (Gwenddalou), son of Ceido, opposed a joined force of Peredur and Gwrgi (the sons of Eliffer and his cousins). Rhydderch the Generous (Rhydderch Hael) killed Gwenddolau and his warriors kept fighting for a month and a half to honor their slain leader.
Merlin was present at the battle, fighting on Gwenddolau’s side in the Welsh verses and with Rhydderch and Peredur in Geoffrey’s Vita Merlini. Merlin is said to have won a golden torc (a necklace or armband made of twisted metal), was driven mad - either by the sight of all the dead, by an apparition he saw in the sky blaming him for the deaths, or by the fact that he killed his nephew - and thereafter roamed the Caledonian Wood (Caledon Wood) (Celyddon, Silva Caledonaiae, or Cat Coit Celidon), becoming a hermit.