Battle of Farsetmore The Battle of Farsetmore was fought near Letterkenny in County Donegal , north - western Ireland , on 8 May 1567 , between the O ' Neill and O ' Donnell Túath . Shane O ' Neill , chief of the O ' Neills of Tyrone , was defeated by Aodh mac Maghnusa Ó Domhnaill ( Hugh O ' Donnell ) and the O ' Donnells freed themselves from O ' Neill aspirations of ruling Ulster as its King . " If Elizabeth , your mistress , is Queen of England , I am O ' Neill , King of Ulster ; I never made peace with her without having been previously solicited to it by her . I am not ambitious for the abject title of Earl . . . . I have gained that kingdom by my sword , and by the sword I will preserve it . ' Shane O ' Neill ' s response to Queen Elizabeth message offering him an English title . Background . Shane O ' Neill had , in the previous 20 years , eliminated his rivals within the O ' Neills and asserted his authority over neighbouring clans ( or " septs " ) the MacDonnells in Antrim and O ' Donnells in Donegal . In 1566 , the English Lord Deputy of Ireland , Henry Sidney , gave military support to the O ' Donnells against O ' Neill , who was regarded as a destabilising and anti - English power in the north of Ireland . O ' Neill forced out these English troops , but the new O ' Donnell chieftain , Hugh O ' Donnell , took the opportunity to assert his independence and raided O ' Neill ' s lands at Strabane . In response , O ' Neill mustered his armed forces and marched into O ' Donnell territory . The battle . O ' Neill crossed into Tir Connell ( O ' Donnell territory ) the traditional way by crossing the River Swilly at an Fearsaid mhór ( known as Porterfields to - day ) ; this is about 3 km East of the modern town of Letterkenny . O ' Donnell had advance warning of this impending incursion so had prepared for the forthcoming attack by dispatching messengers to all his people . Both sides were not equal in size O ' Neills army is estimated at 2 , 000 men and were composed of Cavalry ( Nobility ) , Gallowglass , Kearn and a small body of English soldiers who had deserted to him to provide modern weapon skills to his host . O ' Donnells initial forces was only about 40 - foot and 80 horse ( his personal guard ) . O ' Donnell ' s horsemen harassed O ' Neill ' s men immediately after his fording of the river , leaving O ' Donnell a short breathing space to locate his small force in a more defensible position , at Magherennan ( near the entrance to the Letterkenny Rugby club to - day ) . When their lord was in position the O ' Donnell cavalry withdrew and there O ' Donnell awaited his reinforcments . While his opponent waited , O ' Neill set up his camp in Cluain Aire beside the River to cover the ford . When finally O ' Donnells troops did arrive they numbered 400 Gallowglass from all the MacSweeney septs . With this virtual parity in the ( usually ) decisive heavy infantry the O ' Donnell host proceeded to advance on O ' Neill ' s camp . Shane when first perceiving their attack said : ‘ It is very wonderful and amazing to me that those people should not find it easier to make full concessions to us , and submit to our awards , than thus come forward to us to be immediately slaughtered and destroyed . ’ AFM 1563 This statement , made just as the armies met , must have been a late attempt to put heart into his own surprised army . Significantly the main O ' Donnell war host had employed rising ground to successfully cover their advance until it was far too late for O ' Neill to deploy his own Gallowglass spars into proper line of battle to hold the enemy while the O ' Neill horse mounted up . The O ' Neill army were caught utterly unprepared , in much the same way as O ' Neill himself had taken a MacDonnell host by surprise at Glentaisie in 1565 . Despite the element of surprise and O ' Neill ' s lack of manouvre room , the resistance of the surprised O ' Neill Gallowglass in this encounter battle was at first successful for the Four Masters state that the action lasted " for a long time . " Eventually , with their loose protective screen of gallowglass cut down , a panicked rout of Shane ' s force ensued . The O ' Donnell pressure of attack continued so fiercely that the broken O ' Neill host was forced back on the ford and attempted to recross the Swilly . As the tide was now coming in , many of them to simply drowned in the speeding rush of waters ( 4 – 7 knots average ) . O ' Neill ' s losses are estimated by their enemies at 1 , 400 men killed and no prisoners are mentioned , although the English sources note a more credible total of 680 dead . With many of his most senior commanders and advisors killed amid the chaos of the first onslaught , O ' Neill himself escaped the final slaughter with the timely aid of a party of the Gallaghers . They guided him to Ath an Tairsi ( Ford of protection ) near Grieve Smith in Oldtown to - day , ( not to be confused with Scarrifholis which is further up the river ) where they escorted him to his own territory and relative safety . The aftermath . Many of the Donnelleys , Shane ' s foster family and the source of his strongest support , had defended him to the last and were decimated at Farsetmore . Abandoned by his tanisté and all of his Urríthe , literally under - kings , and with the destruction of his army , the ' most powerful force Gaelic Ireland had yet witnessed ' , Shane began looking for a mercenary force to sustain him until he could make good his losses . With all other options closed he turned to a warband hired to fight against him the previous winter by William Piers from among the MacDonald ' s of Dunnyveg . He arrived at their camp at Cushendun with a small retinue , during their negotiations an altercation occurred , in which Shane was killed . Despite being engineered by Piers , this assassination has gone down in history as retribution for Shane ' s military action against the MacDonalds in 1565 . Shane was buried in a place called CrossSkern Church at Ballyterrim townland in the hills above Cushendun , later his remains were exhumed his head then being sent to Dublin .