Leath Cuinn and Leath Moga

Leath Cuinn (Conn's Half) and Leath Moga (Mug's half) are legendary ancient divisions of Ireland, respectively north and south of a line corresponding to the Esker Riada running east–west from Dublin Bay to Galway Bay.

Thereafter the provinces of Ireland were grouped as follows: To solidify the arrangement, Conn's daughter Sadb was married to Ailill Aulom, son of Mug Nuadat.

Their son was another Éogan Mór, founder of the Eóganachta dynasty which ruled Munster.

David Sproule of the Dublin Institute for Advanced Studies suggests the names Leath Cuinn and Leath Moga originally had their literal meaning "Head Half" and "Slave Half", with the figures of Conn and Mug Nuadat created centuries later as etiological myth, elaborated by the Eóganachta to bolster their territorial claims.

This was altered when the 1152 Synod of Kells separated the provinces of Tuam and Dublin from Armagh and Cashel respectively.