Towards the end of the great cattle raid, after endless minor battles and while the Ulster champion Cúchulainn was engaged in combat, the army of Queen Medb of Connaught finally took the famed Brown Bull of Cooley from his guardians. The task was not simple for one of the herdsmen made a stand at a narrow pass, but Medb's army drove the bull and his cows towards him and they trampled him thirty feet into the ground and made shreds of his body.
The men of Ireland brought the bull to Medb and Ailill in their camp but there was little rejoicing as they had lost so many good warriors and the fighting still continued. When both sides of the conflict were reduced to almost nothing and the men of Ireland were in retreat to Connaught, Medb sent the bull to Cruachu together with fifty of his heifers and eight messengers so that whether the army reached home or not, at least the Brown Bull - Donn Cuailnge would arrive there as she had promised.
Then her issue of blood came upon her and she sent Fergus to cover the retreat.
'By my conscience,' said Fergus 'it is ill-timed.'
'I must pass my water,' Medb replied 'or I'll die.'
Fergus complained bitterly but he went with Medb and shielded her from the view of the retreating army and Medb passed her water and it made three trenches in each of which a household could fit. Cúchulainn came upon her as she was thus engaged but did not wish to strike her from behind and Medb using her womanly wiles used the opportunity to ask him to let her army pass freely until they had gone westward past the Shannon river.
'I grant it,' replied Cúchulainn, and not only that he protected them as they passed by.
Fergus surveyed the sorry sight of all the wounded warriors as they travelled slowly westward. He sighed and went to Medb and said 'This is what happens when an army is led by a woman. You're like a mare leading a band of foals into unknown territory. There's no one to lead and counsel this army and that's why they were plundered and destroyed...'
Medb paid no attention to his rebuke, she gathered what remained of her army and returned to Connaught. When the Donn Cuailnge saw the new surroundings he was in he bellowed loudly three times. The Finnbennach grazing on what he considered to be his territory heard his rival and tossed his head violently and came forward to Cruachu to meet him.
'There is going to be a fight,' the men of Ireland said to each other. No-one was very anxious to watch. The bulls were very dangerous and it was going to be a fight to the death.
There was a man in Cruachu called Bricriu, he was very unpopular with everyone. He had come to Fergus the year before begging for help because his goods had been stolen and Fergus, sorry for him, had taken him into his service. Bricriu had not been grateful, he had insulted Fergus and picked a quarrel with him over a game of chess and Fergus in a rage had struck him so hard that one of the chess-pieces had lodged in his head. During the whole war with Ulster, Bricriu had been convalescing in Cruachu and it was only on the day of the army's return that he got up from his sick-bed.
'Bricriu can be the eye-witness to this fight as he treats his friends and his enemies equally badly, he'll be an excellent referee' said the men of Connaught. Bricriu was brought reluctantly to a gap in the fortifications behind which the Connaught men were sheltering and was told to report on the battle of the bulls.
The bulls faced each other and pawed the ground. Earth flew up over their shoulders and down their backs and their eyes blazed like distended balls of fire. Their cheeks and nostrils swelled like bellows in a forge and they rushed towards each other and collided with a crashing noise. They began to gore and tear at each other and then the Finnbennach with the advantage of being on home-ground, and relying on the confusion of the Donn Cuailnge after his lengthy travels, lunged sideways at the brown bull and thrust his horn into his side. Locked together they rushed violently to the place where Bricriu stood, and before he could move their hooves planted him a man's length into the ground.
They stayed locked together, with the brown bull's hoof planted onto the horn of the white one, for a full day and Fergus, tired of this dead-lock took his spear and slit the back of the Donn Cuailnge in three places.
'You're not much of a bull,' he taunted, 'the Finnbennach is only a calf but he's got the better of you.'
The Donn Cuailnge heard the challenge clearly for he was once in human form. He roared with rage and attacked the Finnbennach with renewed vigour. They fought long and loud until night fell and then all that the men of Ireland could do was listen to the noise and the destruction. That night the bulls travelled the whole of Ireland, fighting over every inch of it. The next morning the men of Ireland went to see the result of the battle.
They saw the Donn Cuailnge coming past Cruachu from the west with the Finnbennach a mangled mass on his horns but at first they could not decipher which bull was which so covered in blood were they.
'Leave him alone,' said Fergus 'whichever bull it is leave him alone in his triumph.' He paused and said 'A mad bull, I have a feeling that whatever happened last night will pale in comparison to what will be done now.'
The Donn Cuailnge came closer. He stamped his foot and shook himself then turned his right side to Cruachu and left a heap of Finnbennach's liver on the ground. He moved on to drink in Finnlethe and left the Finnbennach's shoulder blade behind him there, and then he came to the brink of the Shannon and left the loin of his enemy on the bank. And the place was afterwards called Áth Luain, the Ford of the Loins.
He travelled eastwards into Meath and there he left the rest of the Finnbennach's liver. He tossed his head fiercely and shook of the rest of the mangled bull over Ireland. He threw a thigh as far as Port Láirge, and his rib cage as far as Áth Cliath and after that he faced north and home.
He recognised the land of Cuailnge. It was a land of keening women and children lamenting the loss of their fathers and their sacred bull and he could hear them from afar. They recognised him too and stopped their weeping when they saw him approaching.
Unfortunately the Donn Cuailnge had gone insane with all his trials, and he attacked the women and children who were there to welcome him home, and killed them in their hundreds. And when it was over he turned his back on their mangled bodies and set his face towards the hills, and he was overcome with so much emotion that his heart broke like a nut in his breast and he at last lay down and the life left his body. And there was a deathly silence all around