Muirchertach undertook a "circuit of Ireland" at the head of his army, a campaign commemorated in later verse, during which he took Cellachán prisoner (actually given up to the High King by his own people).
Cellachán had returned to Munster by 944, and perhaps earlier, as in that year he defeated Cennétig mac Lorcáin and killed two of his sons at the battle of Gort Rottacháin.
It may be that the conflict had begun earlier as Dál gCais traditions have Cennétig defeat Cellachán at a battle fought near Lough Saighlenn, somewhere in Munster.
The Caithréim portrays the Eóganachta, and Cellachán in particular, fighting against Norsemen invaders, but also gives credit to the Dál gCais ancestors of Muirchertach.
It is thought that this is related to the contemporary threat posed to the Munster families by the Connacht king Toirdelbach Ua Conchobair.