This, and the news than Flann and the Uí Néill had come to Cerball's aid, led to desertions from Cormac's army, but he continued to march to Leinster and met Cerball and Flann at "Bellach Mugna" (Bellaghmoon, in the south of modern County Kildare). The "Fragmentary Annals" say that "the men of Munster came to the battle weak and in disorder" and they quickly broke and fled the field. Many were killed; Cormac was among them after he broke his neck from falling off his horse. Flaithbertach was captured.