Battle of Curlew Pass The Battle of Curlew Pass was fought on the 15th of August 1599 , during the campaign of the Earl of Essex in the Nine Years ' War , between an English force under Sir Conyers Clifford and a rebel Irish force led by Hugh Roe O ' Donnell . The English were ambushed and routed while marching through a pass in the Curlew Mountains , near the town of Boyle , in northwestern Ireland . The English forces suffered heavy casualties . Losses by allied Irish forces were not recorded but were probably minimal . Campaign . In April 1599 , the Earl of Essex landed in Ireland with over 17 , 000 troops and cavalry to put down the rebellion of Hugh O ' Neill and Red Hugh O ' Donnell , which had spread from Ulster to all Ireland . To this end , he supported an Irish enemy of O ' Donnell ' s , Sir Donogh O ' Connor ( O ' Connor Sligo ) , encouraging him to repossess those territories of his in Sligo that O ' Donnell had occupied . Sligo was an excellent advance base , with Ballyshannon 20 miles to the north - east commanding an important river - ford at the principal western passage into O ' Donnell ' s country in Ulster . English military advisers had long urged the government councils in Dublin and London to capture these strategic points . O ' Connor ' s brother - in - law , Tibbot na Long Burke ( son of Gráinne O ' Malley ) , was appointed joint - commander with an English captain of a force sailing from Galway , and O ' Connor was expected to receive them in Sligo . However , O ' Donnell quickly besieged O ' Connor at Collooney Castle with over 2000 men in an effort to starve him out , and Essex was put on the back foot . Essex had no option but to support the besieged O ' Connor , one of the few Gaelic chieftains the crown could rely upon for support . He ordered the experienced Sir Conyers Clifford , who was based in Athlone , to relieve the castle with 1 , 500 English infantry and 200 cavalry . It was hoped that the operation would also distract the chief rebel , O ' Neill , and afford the crown an opportunity to march into his Ulster territory across its south - eastern border . O ' Donnell left 300 men at Collooney Castle under his cousin , Niall Garbh O ' Donnell , and sent another 600 to Sligo town to prevent the landing of English reinforcements under Tibbot na Long . He then marched to Dunavaragh with 1 , 500 of his men , where he was joined by additional forces under local chieftains Conor MacDermott and Brian Oge O ' Rourke ( son of Brian O ' Rourke ) . The Irish then carefully prepared an ambush site in the Curlew Mountains , along the English line of march . O ' Donnell had trees felled and placed along the road to impede their progress . When he got word of the English passing through Boyle , O ' Donnell positioned his men . Musketeers , archers and javelin men were placed in the woods alongside the road to harass the English . The main body of Irish infantry , armed with pikes and axes , were placed out of sight behind the ridge of the mountain . The battle . In hot harvest weather , Clifford ' s force marched from Athlone through Roscommon , Tulsk and Boyle . At 4pm on August 15 , they reached the foot of the Curlew Mountains ( highest point 860 feet ) , which had to be crossed before Sligo could be approached . The expedition was poorly supplied , and Clifford ' s men were tired and hungry , and probably in no fit state to continue . But Clifford had received false intelligence that the pass was undefended , and he therefore chose to seize the opportunity and march across , promising his troops plenty of beef in the evening . This meant that his men missed out on the rest that had been planned for them in Boyle , whereas the Irish were well fed and prepared . The English came under gunfire , arrow and javelin attack as soon as they reached the first of O ' Donnell ' s barricades , between Boyle and Ballinafad . The barricade was immediately abandoned by the Irish but as the English moved past and proceeded up the hill they sustained further casualties . The road consisted of " " stones of six or seven foot broad , lying above ground , with plashes of bog between them " " , and was lined with woodland on one side . The further the English advanced , the more intensive the rebels ' fire became , and some English soldiers began to lose their nerve and slip away . Eventually , there was a firefight , lasting about 90 minutes , at the end of which the English vanguard had run out of gunpowder . The commander of the vanguard , Alexander Radcliffe , could no longer control his troops . They wheeled about in a panic and collided with the main column , which broke and fled . The commander led a charge with his remaining pikemen but was shot dead . With the English ranks in disarray , the main body of Irish infantry , which had concealed itself on the reverse slope of the hill , closed in and fought hand to hand . Clifford tried to regain control over his men , but appeared overcome by his circumstances . He managed to rally himself and was killed by a pike - thrust as he rushed the enemy . The English were routed , but the situation was prevented from becoming a complete disaster for them when the commander of the horse , Sir Griffin Markham ( with John Harington in his ranks ) , charged uphill - " " amongst rocks and bogs where never horse was seen to charge before " " - and temporarily drove the rebels back . Though the actions of the English cavalry allowed many of their foot soldiers to escape , Clifford ' s men were pursued as far as the town of Boyle , where they found shelter in Boyle Abbey . About 500 English were killed in the battle . Irish losses were not recorded , but were probably small , having been firing from prepared positions and then routing a disorganised and demoralised enemy . Aftermath . Clifford ' s head was cut off and delivered to O ' Donnell - who had remained nearby , but without taking part in the fight . While the head was brought to Collooney Castle to intimidate its defenders , the trunk was carried by MacDermott to the monastery of Lough Key , where he hoped to use it to ransom his own prisoners . At last , the trunk was given a decent burial in the monastery , and it was noted at the time that Clifford had lately dreamed of his own capture by O ' Donnell and of being carried by monks into their convent . O ' Connor Sligo surrendered the castle shortly afterwards and reluctantly joined with the rebels . After the victory , there was a noticeable increase in the rate of desertion by Irish troops from the ranks of Essex ' s army , and the earl ordered that the surviving troops be divided up as fit only to hold walls . The battle was a classic Gaelic Irish ambush , similar to the battle of Glenmalure in 1580 or the battle of the Yellow Ford in 1598 . According to the Annals of the Four Masters , the victory was put down to the intercession of the Blessed Mary , rather than to arms . But Clifford had been overconfident - a trait in him that Essex once warned against - and it is clear that English military commanders were choosing to learn the hard way about the increased effectiveness of Irish rebel forces . The Queen ' s principal secretary , Sir Robert Cecil , rated this defeat ( and the simultaneous defeat of Harrington in Wicklow ) as the two heaviest blows ever suffered by the English in Ireland , and sought to lay the blame indirectly on Essex . It left O ' Donnell and O ' Neill free from any threat from the Connacht side , and rendered a land - based attack through Armagh highly improbable , a factor that weighed with Essex as he marched northward later in the year and entered a truce with O ' Neill . In August 1602 , the Curlew Pass was the scene of the last victory won by the rebels during the war , when a panicking English force was again routed and suffered significant losses ; this time , the rebels were led by Rory O ' Donnell ( and with him , O ' Connor Sligo ) who commanded 400 musketeers . Today the battlefield at Curlew Pass is overlooked by an impressionistic sculpture by Maurice Harron called " The Gaelic Chieftain " , unveiled in 1999 .