When Taran and his Companions came upon the wall during their pursuit of the Cauldron-Born on their way to Annuvin, they saw that the barrier was crumbling and that, if they meant to use it to turn back the deathless warriors, the many gaps in the stonework would have to be shored up with branches and weapons. Here Taran's force of Commot men fought a desperate battle against the Cauldron army. Many lives were lost in the effort, including that of Coll Son of Collfrewr, who from atop the wall single-handedly turned back a troop of Cauldron warriors.
Taran quickly joined his mentor in the successful defense, but his help came too late: Coll had suffered mortal wounds. Taran buried Coll at the foot of the Ruined Wall, in a grave he hollowed out of the harsh, red earth with his own hands, under a cairn of stones collected from the crumbling wall by the companions.
There Taran recalled his promise to dig and weed in Caer Dallben alongside Coll. There, too, he mourned his mentor till night fell, after his friends and warriors had ridden into the hills to pursue the Cauldron-Born.