From An Illustrated History of Ireland by Margaret Anne Cusack
« start... Chapter XIII. ...continued
There is some question as to the precise year in which Brian obtained or usurped the authority and position of Ard-Righ: A.D. 1002, however, is the date most usually accepted. He was probably about sixty-one years of age, and Malachy was then about fifty-three.
It will be remembered that Brian had married the Lady Gormflaith. Her brother, Maelmordha, was King of Leinster, and he had obtained his throne through the assistance of the Danes. Brian was Gormflaith's third husband. In the words of the Annals, she had made three leaps—"jumps which a woman should never jump"—a hint that her matrimonial arrangements had not the sanction of canon law. She was remarkable for her beauty, but her temper was proud and vindictive. This was probably the reason why she was repudiated both by Malachy and Brian. There can be no doubt that she and her brother, Maelmordha, were the remote causes of the famous battle of Clontarf. The story is told thus: Maelmordha came to Brian with an offering of three large pine-trees to make masts for shipping. These were probably a tribute which he was bound to pay to his liege lord. The trees had been cut in the great forest of Leinster, called Fidh-Gaibhli.
Some other tribes were bringing their tree-tributes at the same time; and as they all journeyed over the mountains together, there was a dispute for precedency. Maelmordha decided the question by assisting to carry the tree of the Ui-Faelain. He had on a tunic of silk which Brian had given  him, with a border of gold round it and silver buttons. One of the buttons came off as he lifted the tree. On his arrival at Kincora, he asked his sister, Gormflaith, to replace it for him; but she at once flung the garment into the fire, and then bitterly reproached her brother with having accepted this token of vassalage. The Sagas say she was "grim" against Brian, which was undoubtedly true. This excited Maelmordha's temper. An opportunity soon offered for a quarrel. Brian's eldest son, Murrough, was playing a game of chess with his cousin, Conoing; Maelmordha was looking on, and suggested a move by which Murrough lost the game. The young prince exclaimed: "That was like the advice you gave the Danes, which lost them Glen-Mama." "I will give them advice now, and they shall not be defeated," replied the other. "Then you had better remind them to prepare a yew-tree  for your reception," answered Murrough.
Early the next morning Maelmordha left the place, "without permission and without taking leave." Brian sent a messenger after him to pacify him, but the angry chief, for all reply, " broke all the bones in his head." He now proceeded to organize a revolt against Brian, and succeeded. Several of the Irish princes flocked to his standard. An encounter took place in Meath, where they slew Malachy's grandson, Domhnall, who should have been heir if the usual rule of succession had been observed. Malachy marched to the rescue, and defeated the assailants with great slaughter, A.D. 1013. Fierce reprisals now took place on each side. Sanctuary was disregarded, and Malachy called on Brian to assist him. Brian at once complied. After successfully ravaging Ossory he marched to Dublin, where he was joined by Murrough, who had devastated Wicklow, burning, destroying, and carrying off captives, until he reached CillI Maighnenn (Kilmainham). They now blockaded Dublin, where they remained from St. Ciaran's in harvest (Sept. 9th) until Christmas Day. Brian was then obliged to raise the siege and return home for want of provisions.
The storm was now gathering in earnest, and the most active preparations were made on both sides for a mighty and decisive conflict.
 Fifty-three.—See Dr. O'Donovan's note to Annals, p. 747.
 Fidh-Gaibhli.—Now Feegile, near Portarlington.
 Given.—The Book of Rights mentions, that one of the rights to which the King of Leinster was entitled from the King of Ireland, was "fine textured clothes at Tara," as well as "sevenscore suits of clothes of good colour, for the use of the sons of the great chief tain."—Book of Rights, p. 251. From the conduct of Gormflaith, as related above, it is evident that the tunic was some token of vassalage.
 Murrough.—He was eldest son by Brian's first wife, Môr. He had three sons by this lady, who were all slain at Clontarf.
 Yew-tree. —This was a sharp insult. After the battle of Glen-Mama, Maelmordha had hidden himself in a yew-tree, where he was discovered and taken prisoner by Murrough.