Despite a somewhat uncertain relationship the Great Earl was King Henry VII’s man in Ireland. He was charged with ensuring that no other than himself should dictate the state of the King's affairs in this Country. Something of a poacher turned gamekeeper the Great Earl would brook no rivals. Ulick Burke had thrown down the gauntlet however by seizing three castles belonging to the O’Kellys of south Galway and also taking under his control the Royal city of Galway. Ironically Ulick was also Garret’s son in law! While not a certainty he seems to have fallen out with his wife Eustacia and she had returned to be under her fathers roof. The O’Kellys also appealed to him for the restitution of their fortresses.
He decided to lead an Army to the West and settle the issue through battle. He led a formidable force with him, perhaps as many as 6,000 warriors and many of them the iron clad Gallowglass who dominated the battlefields of Ireland in the latter Middle Ages. To oppose him Ulick gathered a similar type of force but he could not match the Great Earls resources or network of connections. He had maybe about 4,000 men in the field on the day of battle. The Great Earl mustered forces from Leinster and Ulster with some Connacht allies too. Burkes’ own force was comprised of his retinue from south Galway, and his allies from northwest Munster. To the Gaels it seemed that the great wars between the provincial kings of old in the days before the English arrived had returned. But to Garret it was more like a version of a suppression of a rebellion against Royal authority that the King of England might engage upon across the water. In truth there was a mixture of both these analogies in what happened.
In the event Garret Fitzgerald beat his opponent decisively and retook Galway from Ulick Burke. The battle though was bloody and hard fought – ‘a dour struggle’. Essentially an infantry battle both sides hacked and slashed at each other to bring the other down. It is also the first battle to record the use of a gun - a Palesman beat out his opponent’s brains with the butt of his piece! It was really a medieval battle of the old style and the last great one of its kind. Both sides clashed early in the morning and it was late in the day before the remnants of Burkes’ much depleted host broke and ran. The Geraldine force camped on the battlefield that night to collect booty and bring in the stragglers. The Great Earl proceeded the next day to enter the City of Galway in Triumph and received the keys of the metropolis from the grateful Mayor.
A fierce battle was fought between them, such as had not been known of in latter times. Far away from the combating troops were heard the violent onset of the martial chiefs, the vehement efforts of the champions, the charge of the royal heroes, the noise of the lords, the clamour of the troops when endangered, the shouts and exultations of the youths, the sound made by the falling of the brave men, and the triumphing of the nobles over the plebeians. The battle was at length gained against Mac William, O'Brien, and the chiefs of Leath-Mhogha; and a great slaughter was made of them; and among the slain was Murrough Mac-I-Brien-Ara, together with many others of the nobles. And of the nine battalions which were in solid battle array, there survived only one broken battalion. A countless number of the Lord Justice's forces were also slain, though they routed the others before them. It would be impossible to enumerate or specify all the slain, both horse and foot, in that battle, for the plain on which they were was impassable, from the vast and prodigious numbers of mangled bodies stretched in gory litters; of broken spears, cloven shields, shattered battle-swords, mangled and disfigured bodies stretched dead, and beardless youths lying hideous, after expiring.
Annals of the Four Masters