TheBattle of Mag Femen^{[nb 1]} took place on 22 August 917 between theVikings of theUí Ímair, led byRagnall, a grandson ofÍmar, and theIrish of theNorthern Uí Néill, led byNiall Glúndub,High King of Ireland. It was one of two battles involving the Uí Ímair that year, the other being theBattle of Confey, which occurred as a result of the Uí Ímair trying to retake theKingdom of Dublin which they had lost in 902. The battle began when Niall Glúndub's forces attacked a Viking army at a site identified by theannals as Topar Glethrach in Mag Femen. The Irish initially inflicted the majority of the casualties, but late in the day a host of more troops led by Ragnall reinforced the Viking army, securing victory for the Uí Ímair.

The rulingVikings ofDublin, theUí Ímair, had been expelled from the city in 902 by a joint force led by Máel Finnia mac Flannacán, overking ofBrega andCerball mac Muirecáin, overking ofLeinster.^{[nb 2][2]} However, this expulsion was temporary and Viking raids continued on Irish settlements. In 914 a large Viking fleet sailed to the previously Viking-controlled city ofWaterford, and the following year more Vikings settled inLimerick, though Dublin itself remained outside Uí Ímair control.^[3] In 917 two prominent members of the Uí Ímair,Ragnall andSitric Cáech, grandsons ofÍmar, sailed separate fleets to Ireland, Ragnall landing at Waterford and Sitric Cáech landing at Cenn Fuait inLeinster.^{[nb 3][5]} Several nativeIrish kings gathered forces to try to drive off the Vikings once more, includingNiall Glúndub, overking of the NorthernUí Néill andHigh King of Ireland, andAugaire mac Ailella, overking of Leinster. The Vikings met Niall Glúndub and the men of the Uí Néill in battle at Mag Femen inCounty Tipperary.^[5]

According to theAnnals of Ulster the army ofNiall Glúndub marched south to war against the Uí Ímair and halted on 22 August at Topar Glethrach in Mag Femen. A force of Vikings was nearby, and the Irish began the battle by attacking that morning. The battle lasted until the evening, with around 100 casualties between the two sides, most of them on the Viking side. The tide was turned when a large number of reinforcements led by Ragnall arrived, and the Irish fled back to their camp.^[6] TheAnnals of the Four Masters give a similar but slightly different account of the battle. In that account one thousand one hundred men died in the battle, not one hundred, and it also says that the Irish fled the battle before the arrival of Ragnall. TheFour Masters account also enumerates several casualties not listed in theUlster account: the chief ofCairrge Brachaidhe; Máel Finnén mac Donnagáin, chief of Úi Cearnaigh; and Fergal mac Muirecáin, chief of Uí Chreamhthainn.^[7]

Both accounts agree that after the battle a small force led by Niall Glúndub encamped against Ragnall's army for twenty nights. Niall sent word toLeinster that they should bring an army to lay siege to the Viking force. The Leinstermen did so, but their force was destroyed and their kingAugaire mac Ailella was slain by the army ofSitric Cáech at theBattle of Confey.^[8] Augaire's death marked the end of effective opposition to the Vikings' return to Ireland. Sitric led his men on a triumphant return toDublin, where he established himself as king, while Ragnall returned to England and soon becameKing of Northumbria.^[5]

• "Annals of the Four Masters".Corpus of Electronic Texts (16 December 2013 ed.).University College Cork. 2013. Retrieved5 March 2015.
• "Annals of Ulster".Corpus of Electronic Texts (15 August 2012 ed.).University College Cork. 2012. Retrieved5 March 2015.
• "Dictionary of the Irish Language".Electronic Dictionary of the Irish Language (2012 ed.).Royal Irish Academy. 2012. Archived fromthe original on 2 January 2015. Retrieved5 March 2015.

• Bartlett, Thomas; Jeffery, Keith (9 October 1997).A Military History of Ireland. Cambridge University Press.ISBN 978-0-521-62989-8.
• Downham, Clare (2007).Viking Kings of Britain and Ireland: The Dynasty of Ívarr to A.D. 1014. Edinburgh:Dunedin Academic Press.ISBN 978-1-903765-89-0.
• Duffy, Seán (15 January 2005).Medieval Ireland: An Encyclopedia. Routledge.ISBN 978-1-135-94824-5.
• Forte, Angelo; Oram, Richard D.; Pedersen, Frederik (5 May 2005).Viking Empires. Cambridge University Press.ISBN 978-0-521-82992-2.
• O Croinin, Daibhi (16 December 2013).Early Medieval Ireland, 400–1200. Routledge.ISBN 978-1-317-90176-1.

• CELT: Corpus of Electronic Texts atUniversity College Cork. TheCorpus of Electronic Texts includes theAnnals of Ulster andthe Four Masters, theChronicon Scotorum and theBook of Leinster as well as Genealogies, and various Saints' Lives. Most are translated into English, or translations are in progress.

• 910s conflicts
• Battles involving the Vikings
• Battles involving the Uí Néill
• Viking Age in Ireland

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• Short description matches Wikidata
• Use dmy dates from June 2015