Here follows first a brief summary of the adventure which led to the death of Conchubhar.
Now at that time, in order to incite champions to be brave in conflict, it was customary to give a champion's prize as a token of victory to him who proved the stronger in single combat, and who vanquished his adversary in the field of valour. From this custom there arose a contest for the champion's prize between Conall Cearnach, and Cuchulainn and Laoghaire Buadhach in Eamhain. And Conall asked for the brain of Meisceadhra, a stout Leinster champion whom he had himself slain in single combat; and when the brain of that valiant man was exhibited, Laoghaire and Cuchulainn ceased from their contest with Conall, as they judged that neither of them had ever done so great a deed of bravery or valour. It was the custom at that time that when any champion slew in battle another champion of great fame, he took the brain out of his head and mixed it with lime, so that he had it in the shape of a hard round ball to show at meetings and public assemblies as a trophy of valour. And when two jesters whom Conchubhar kept noticed how highly everyone prized the brain, they stole it the next day from Conchubhar's Craobhdhearg. Now there were three dwellings in Eamhain in Conchubhar's time, namely, Broin Bhearg and Craobh Dhearg and Craobh Ruaidh. In the first house were their wounded; and it was called Broin Bhearg, because the wounded who were in it felt sorrow and distress from the piercing pain of the wounds, and of the distempers from which they suffered therein. In the second house, which was called Craobh Dhearg, were kept in safety the arms and precious valuables; and accordingly Meisceadhra's brain was placed there for security as any other precious valuable. The third house that Conchubhar had was called the Craobh Ruaidh. It was in it himself and all his warriors used to be served.
As to the two jesters, having carried off the brain of Meisceadhra from the Craobh Dhearg as we have said, they went on the green of Eamhain, and set to bandying the brain from hand to hand like a ball, when a fierce wolf of evil to the Ultonians, to wit, Ceat son of Magha, a valiant Connaughtman, came and coaxed the brain of Meisceadhra from the jesters, and took it with him to Connaught; and as often as he went to battle or contend against the Ultonians he was wont to have the brain of Meisceadhra at his girdle in the hope of bringing disaster on the Ultonians. For it was foretold that Meisceadhra would avenge himself on the Ultonians after his death; and he thought it was by means of the brain this prophecy would be fulfilled. Whence Ceat was wont to carry the brain of Meisceadhra about with him in the hope of slaying some one of the nobles of Ulster with it. Now Ceat, accompanied by a large host, went to plunder Ulster, and carried off a large herd of cattle from Feara Rois in Ulster; and he was pursued by a large force of Ultonians; and the men of Connaught flocked eastward to assist Ceat, and Conchubhar went westward to help the Ultonians. And when Ceat heard that Conchubhar was in pursuit, he sent word to the women of Connnaght who were on a hill watching the two hosts asking them to entice Conchubhar to visit them, as he was a jovial, affable man, for the Ultonians would not permit him to take part in the battle against the men of Connaught.
Now when Conchubhar heard that the women wished to see him, he set out alone from the height on which he was to visit them; while Ceat, on the other hand, went secretly and got into the midst of the women waiting in readiness to kill Conchubhar. When, therefore, Conchubhar was approaching the women, Ceat arose and arranged the brain of Meisceadhra in his sling to slay Conchubhar. But when the latter saw Ceat, he retreated to the midst of his own people; and as he was proceeding to Doire Da Bhaoth, Ceat hurled the brain of Meisceadhra after him from his sling, and struck him on the crown; and his brain-pan was broken by that cast, and the brain of Meisceadhra clung to his skull; and thereupon his followers came up to protect him against Ceat. They then sent for Finghin Faithliaigh; and when he arrived, he said that if that ball were extracted from his head he would instantly die. "We had rather," said they all, "that our king should have a blemish than that he should die." Finghin cured him, and then told him not to get into a passion, to avoid sexual intercourse, to avoid riding on horseback, to abstain from violent exertion -- otherwise, that by the repelling motion of his own brain, he would hurl the ball from his head and die.
He was seven years in this state up to the Friday on which Christ was crucified, according to some seanchas. And when he saw the unwonted transformation of the elements and the darkening of the sun with the moon full, he inquired of Bacrach, a Leinster druid who was with him, what was the cause of that unwonted change in the luminaries of heaven and earth. "It is that Jesus Christ the Son of God is being put to death now by the Jews," replied the druid. "That is a pity," said Conchubhar; "and if I were present, I would slay all that are around my King putting Him to death." And with that he drew forth his sword, and went into an oak-wood hard by, and set to cutting and felling it, saying that, if he were amongst the Jews, he would treat them in the same way; and through the strength of the fury that seized him the ball bounded from his head, and a portion of his brain followed it, and with that he died. Coill Lamhruidhe in Feara Rois is the name of that wood-thicket.
After Conchubhar's death, the kingdom of Ulster was offered to whoever should carry his body to Eamhain without resting. A servant of Conchubhar's named Ceann Bearroide was present, and in the hope of obtaining the kingdom, took up the body stoutly and carried it to Ardachadh, in Sliabh Fuaid, but there his heart broke and he died. And this event has given rise to the saw which says that one seeks the kingdom of Ceann Bearroide when one aspires ambitiously to a rank which it is beyond his power to attain.
But though authors relate this story of Conchubhar, alleging that he was a contemporary of Christ, still, according to the truth of history, Christ was not born for a long time after Conchubhar; and the truth of this story is that Bacrach, a Leinster druid, foretold through prophecy that Christ the Prophesied One, the Son of God, would be conceived, that He would assume a body, and that the Jews would put Him to death; and through Him the human race would be delivered from the tyranny of the evil one. And when Conchubhar heard this, he became enraged as we have said; and through sympathy with Christ, he set to cut down the wood of Lamhruidhe as if the trees were the Jews; and he died of that effort. And if anyone should deem it strange that Bacrach or any other druid, being Pagan, should foretell the death of Christ, how was it more fitting for the Sybils, who were Pagans, to have foretold Christ before His birth than for Bacrach or any of his kind? Hence the story is not to be thus discredited.