A Gaelic alliance led by Brian O'Neill (High-King of Ireland) and Hugh O'Connor were defeated by the Normans.
O'Neill allied with Hugh McPhelim O'Connor (Aedh mac Fedhlimidh Ua Conchobhair) of Connacht and together with their men went into battle against the Normans.
Many of the Irish clans in Leinster, Ulster, Munster, Meath, and Breifne, which were under Norman rule at the time, provided the Normans with the bulk of their fighting forces, serving as mercenaries and retained bands.
The Annals of Innisfallen state:Brian Ua Neill, king of Cenél Eógain, to whom the Gaedil gave hostages, and who paid-neither tax nor tribute to the king of England, was slain by the Gaedil (Irish) themselves and by some of the foreigners (Anglo-Normans) {at Dún dá Lethglas}.
But one notable thing happened: fifteen men of the nobles of Clann-Cathain were killed on that spot.