Battle of Moyry Pass The Battle of Moyry Pass was fought during September and October 1600 in counties Armagh and Louth , in the north of Ireland , during the Nine Years ' War . It was the first significant engagement of forces following the cessation of arms agreed in the previous year between the Irish leader Hugh O ' Neill and the English Crown commander , the Earl of Essex . The battle was fought by the armies of O ' Neill and the new English commander , Lord Mountjoy , a former follower of the late Earl of Essex . Mountjoy had determined to penetrate O ' Neill ' s heartlands in central and western Ulster . To do this , he needed to penetrate Moyry pass . In the course of a two - week assault on O ' Neill ' s defences at the pass , Mountjoy ' s troops eventually got through the pass and established a garrison near Armagh , but took heavy casualties in the process . Mountjoy ' s main English force then retired with difficulty back to friendly territory in Dundalk . Campaign . Mountjoy ' s strategy for putting down O ' Neill ' s rebellion was to gradually constrict his territory in Ulster by establishing a ring of fortified garrisons on the borders of O ' Neill and his allies . To this end , he had landed seaborne forces at Derry in the north of the province and at Carrickfergus in the east of Ulster . In September 1600 , Mountjoy moved north from Dublin and concentrated at Dundalk , in order to mount an expedition further into Ulster and re - establish a garrison at Armagh , which position had been evacuated by the English Crown forces after O ' Neill ' s victory at the Battle of the Yellow Ford in 1598 . On 17 September 1600 , Mountjoy set out from Dundalk , intending to march to Newry and then on to Armagh . The Moyry Pass ( or " Gap of the North " ) was his feasible only point of entry into Ulster ( much of the terrain being wooded and mountainous ) , and it had been well fortified by O ' Neill with trenches and barricades . The Irish had constructed three lines of trenches , backed up with barricades of earth and stone . On the flanks , the Irish had made further earth and stone works and ' plashed ' ( twisted ) the branches of low - growing trees in order to provide cover for themselves and prevent the English occupying the heights on either side of the Pass . In these positions , they awaited the English assault . The battle . The English force reached the pass on 20 September and set up camp just outside it , to the south , on Faughart Hill . Taking advantage of a misty day on the 25th , an officer named Thomas Williams ( who had commanded the Blackwater Fort during the Battle of the Yellow Ford ) made a sortie into the pass . After heavy fighting , he identified the Irish defence works and returned to the English camp with 12 dead and 30 wounded . For the next six days , heavy rain held up the fighting , until the weather cleared on 2 October . The weather was important because the matchlock muskets of the day would not work in wet conditions . On 2 October , Sir Samuel Bagnall led his regiment of infantry into the Pass at the head of four other regiments . The English breached the first barricade and Thomas Bourke ' s regiment then led the way to the second and third lines of defence . The English took the second line only to find they were in a trap being fired on from three sides . They tried to dislodge the Irish from their remaining positions for three more hours before finally retreating , barely getting out with the Irish in close pursuit . The English admitted 46 killed and 120 wounded , but it is thought that they understated their losses throughout the campaign . On 5 October , Mountjoy tried to bypass the heavily defended Pass by sending two regiments on a flanking march over the hill to the west of the Pass , with one further regiment supported by horsemen advancing up the centre of the Pass . No English regiment made significant gains and , with stiff Irish resistance , the force was forced to turn back . The English reported 50 dead and 200 wounded . By 9 October , an English officer named Geoffrey Fenton complained , " we are now but where we were in the beginning " . Mountjoy , giving up on trying to storm the Pass retired to Dundalk on either the 8th or 9 October . However , on the 14th , word reached the English camp that O ' Neill had abandoned the Pass and retreated to a crannog stronghold at Lough Lurcan . At the time , Mountjoy could not understand why O ' Neill would voluntarily leave such a strong defensive position . The most likely explanation for O ' Neill ' s withdrawal is that he was both short of ammunition and food and feared a flanking attack on his rear from Newry . Moreover , most of his forces were composed of temporary , clan - based levies , who could not be kept together for long . Mountjoy accordingly occupied Moyry Pass on the 17th of October and dismantled the Irish earthworks there . He then marched on to Carrickban , just outside Newry . After a stay at Carrickban , Mountjoy marched to Mountnorris ( halfway between Newry and Armagh ) by Sunday 2 November . There he built an earthwork fort and left a garrison of nominally 400 men in it , under the command of Captain Edward Blaney . Returning to Newry from Mountnorris , the English marched back to Dundalk via Carlingford . On 13 November , during this return march they were again opposed by O ' Neill , close to the Fathom Pass , and suffered 15 – 20 killed and 60 – 80 wounded . Aftermath . The battle of Moyry Pass was basically a stalemate . Mountjoy could not take the Pass , but O ' Neill could not keep his force together long enough to hold it . Mountjoy did establish a garrison at Mountnorris , but still had to retire to Dundalk after taking substantial casualties . Mountjoy claimed his force lost only 200 men killed and 400 wounded in the fighting from 20 September to 13 November , though this may be a considerable underestimate . More , he said , died of disease . The Irish casualties were given by the English as an incredible 900 – 1200 killed and wounded , but this is most unlikely given the fact that the Irish were in a strong defensive position of their own choosing , behind the protection of fieldworks and had lured the English into an ambush which they barely escaped from . These figures probably say more about what Mountjoy wanted the Queen to hear than about the actual casualty figures .