Leath Cuinn

Leath Cuinn (Conn's Half) and Leath Moga (Mugh's half) refers to an ancient division of Ireland.

Leath Cuinn was the island north of the Esker Riada (east-west drumlin belt from Dublin to Galway Bay). Conn Cétchathach, for whom this division is named, was a retrospective ancestor of the Connachta and Uí Néill dynasties.

As a result of the battle of Maigh Nuadad in A.D. 123 where he was defeated by Eoghan Mor (also known as Mug Nuadat, Conn was forced by Mug to accede to the division of Ireland into two half's; the north - taking in Connacht, Ulster and Meath - would be Conn's Half; the south - taking in Munster and Leinster would be Mugh/Mogh's Half. To solidify the arrangement, Conn's daughter Sadbh was married to Oiloill Olum, son of Mogh. The Eoganacht dynasty in Munster claimed, as descendants of Oiloill Olum, the historical right as overkings of Leath Moga (i.e. overlordship of Leinster as well as Munster) in the early medieval age, a claim disputed by the Ui Neill.