Áed Menn (‘stammering’) (d. 738), son of Colcu, king of south Leinster and contender for overkingship of the province, was a member of the Síl Cormaic lineage of Uí Chennselaig. His father Colcu (d. 722) had held the relatively minor kingship of Ard Ladrann, the caput of which was located at a site identified as the ‘moat of Ardamine’ (townland of Middletown, parish of Ardamine, Co. Wexford). Áed had at least two brothers, Bressal and Sechnassach. It appears that he had already achieved prominence in his own right by the time of his father's death. The saga ‘Cath Almaine’, which tells how the Uí Neill king of Tara, Fergal (qv) son of Máel-dúin, was defeated in battle near the Hill of Allen and slain by Áed, credits Áed with kingship of all Leinster. The same tale, however, makes out that Fergal had sought to levy the traditional Uí Neill bóruma (cattle-tribute) on Leinster, which hardly accords with historical reality. Given the strength of the Uí Dúnlainge dynasty under Murchad (qv) son of Bran Mút and his sons, it is difficult to envisage how Áed's authority could, at this stage, have extended beyond the realms of Uí Chennselaig, i.e. from the Wexford coast to the River Barrow. Nonetheless, in 732 Áed was powerful enough to defeat an incursion into Leinster by the Munstermen under their king Cathal (qv) son of Finguine. It is probable that the interests of Áed's dynasty had already become established at Ferns by this time; in any case, his brother Bressal (d. 749) became abbot in 741.
In the course of the 730s Áed Menn emerged as de facto overking of Leinster. Although he is ignored by the later king-lists, the original Annals of Ulster entry on the battle of Áth Senaig (738) indicates that Áed was by then the pre-eminent Leinster king. Áth Senaig (possibly Ballyshannon near Kilcullen, Co. Kildare) marked a signal defeat for the Leinstermen, Áed himself being slain by the Uí Néill king of Tara, Áed Allán (qv) son of Fergal; the Annals of Ulster state that he was beheaded in hand-to-hand combat. It is certainly significant that the leading Uí Dúnlainge dynast of the day, Bran Becc son of Murchad, fell alongside Áed. After the battle the kingship of Uí Chennselaig passed for a time to Áed's brother Sechnassach; later Etarscél son of Áed reigned as king. The dynasty exercised power, however, only within southern Leinster. For the next three centuries the provincial kingship was monopolised by the north Leinster ruling lineages of Uí Dúnlainge.