Áth Senaig’s Broken Leinster
Archived: 1 November 2026
Abstract
In 738, Áed Allán, king of Tara, defeated Leinster at Áth Senaig, probably near modern Kilcullen, killing Áed mac Colggen, Bran Bec and numerous provincial leaders. Annals date the battle to 19 August, although claims of near-total destruction and 9,000 deaths are rhetorical. The defeat intensified Leinster’s succession crisis, weakened Uí Chennselaig, and preceded long Uí Dúnlainge dominance, without conquering the province. Munster’s Cathal mac Finguine also exacted hostages and treasure from Leinster, though chronology is uncertain. Tólae, bishop of Clonard, died, while Cernach of Brega was murdered, illustrating ecclesiastical influence and continuing dynastic instability across Ireland during the year.