Battle of Castlebar The Battle of Castlebar occurred on 27 August 1798 near the town of Castlebar , County Mayo , during the Irish Rebellion of that year . A combined force of 2 , 000 French and Irish routed a force of 6 , 000 British militia in what would later became known as the " Castlebar Races " , or " Races of Castlebar " . Background . The long - awaited French landing to assist the Irish revolution begun by Theobald Wolfe Tone ' s Society of United Irishmen had taken place five days previously on 22 August , when almost 1 , 100 troops under the command of General Jean Joseph Amable Humbert landed at Cill Chuimín Strand , County Mayo . Although the force was small , the remote location ensured an unopposed landing away from the tens of thousands of British soldiers concentrated in the east in Leinster , engaged in mopping up operations against remaining pockets of insurgents there . The nearby town of Killala was quickly captured after a brief resistance by local yeomen . Just south , Ballina was taken two days later following the rout of a force of cavalry sent from the town to oppose the Franco - Irish march . Following the news of the French landing , Irish volunteers began to trickle into the French camp from all over Mayo . The Lord Lieutenant of Ireland , Lord Cornwallis , requested urgent reinforcements from England but in the interim all available forces were concentrated at Castlebar under the command of General Gerard Lake , the victor of the Battle of Vinegar Hill . The build - up of the British forces at Castlebar had reached 6 , 000 soldiers with dozens of artillery pieces and huge cache s of supplies by dawn of 27 August . Preparations . Leaving about 200 French regulars behind in Killala to cover his rear and line of withdrawal , Humbert took a combined force of about 2 , 000 French and Irish on 26 August to march on and take Castlebar . The obvious nature of his objective presented the reinforced British there with the apparent advantage of being able to deploy their forces to face a head - on attack from the Ballina road and their forces and artillery were accordingly arranged . However , locals advised the French of an alternative route to Castlebar through the wilds along the west of Lough Conn , which the British thought impassable for a modern army with attendant artillery train . This route was successfully taken and when Lake ’ s scouts spotted the approaching enemy , the surprised British had to hurriedly change the deployment of their entire force to face the threat from this unanticipated direction . Attack . The British had barely completed their new deployment when the Franco - Irish army appeared outside the town at about 6 . 00 a . m . The newly sited British artillery opened up on the advancing French and Irish and cut them down in droves . French officers , however , quickly identified an area of scrub and undergrowth in a defile facing the centre of the artillery line which interfered with , and provided some cover from , the British line of fire . The French launched a bayonet charge , the ferocity and determination of which unnerved units of the militia stationed behind the artillery . The militia units began to waver before the French reached their lines and eventually turned in panic and fled the battlefield , abandoning the gunners and artillery . Some soldiers of the Longford and Kilkenny militias ran to join the republicans and even joined in the fighting against their former comrades . A unit of cavalry and British regular infantry attempted to stand and stem the tide of panic but were quickly overwhelmed . British retreat . In the headlong flight of thousands of British soldiers , massive quantities of guns and equipment were abandoned , among which was General Lake ' s personal luggage . Although not pursued a mile or two beyond Castlebar , the British did not stop until reaching Tuam , with some units fleeing as far as Athlone in the panic . The panic was such that only the arrival of Cornwallis at Athlone prevented further flight across the Shannon . Although achieving a spectacular victory , the losses of the French and Irish were high , losing about 150 men , mostly to the cannonade at the start of the battle . The British suffered over 350 casualties of which about 80 were killed , the rest either wounded or captured , including perhaps 150 who joined the republicans . Following the victory , thousands of volunteers flocked to join the French who also sent a request to France for reinforcements and formally declared an Irish Republic .