Leath Cuinn and Leath Moga

Leath Cuinn (Conn's Half) and Leath Moga (Mugh's half) are legendary ancient divisions of Ireland.

Map of Gaelic Ireland: Leth Cuinn in yellow, Leth Moga in green.

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.

Ireland's legendary ancient division into Leath Cuinn (Conn's Half) and Leath Moga (Mugh's half) resulted from the battle of Maigh Nuadad in 123 A.D. Conn, defeated by Eoghan Mor (also known as Mug Nuadat), was forced to accede to the division of Ireland into two halves:

• The North - taking in Connacht, Ulster and Meath - would be Conn's Half
• The South - taking in Munster, Osraighe and Leinster - would be Eoghan's Half.

To solidify the arrangement, Conn's daughter, Sadhbh was married to Ailill Aulom, son of Eoghan.

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 Uí Néill.

In the twelfth century, the north-south division of Ireland was used as a basis for the new division of dioceses in Ireland at the Synod of Ráth Breasail.