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The Uí Dúnlainge, from the Old Irish "grandsons of Dúnlaing", were an Irish dynasty of Leinster kings who traced their descent from Dúnlaing mac Énda Niada. He was said to be a cousin of Énnae Cennsalach, eponymous ancestor of the rival Uí Chennselaig.
Their claims to the kingship of Leinster were unopposed after the death of Áed mac Colggen in the Battle of Ballyshannon 738 (Aug 19). The dynasty then divided into three kindreds which rotated the kingship between 750-1050. This is unusual in early Irish history as it was the equivalent of “keeping three oranges in the air” (the east Ulster kingdom of Ulaid also rotated the kingship between families). Fourteen Uí Muiredaig kings (later to become the O'Toole family) were based at Mullaghmast/Máistín nine Uí Faelain kings (later to become the O'Byrne family) were based at Naas/Nás na Ríogh and ten Uí Dúnchada kings (later the FitzDermots) were based at Lyons Hill/ Líamhain nearest to Dublin city.
The Fitzdermots later gave their names to the placenames Dolphin's Barn and Ballyfermot. The influence of the family helped secure place-myths for prominent Kildare landmarks in the heroic and romantic literature such as the Dindeanchas, Dinnshenchas Érenn as one of the “assemblies and noted places in Ireland”. After the death of the last Kildare-based King of Laighin, Murchad Mac Dunlainge in 1042, the Kingship of Leinster reverted to the Uí Cheinnselaig kindred based in the south east.