Medb insisted that she be equal in wealth with her husband, and started the Cattle Raid of
Cooley when she discovered that Ailill was one powerful stud bull richer than her. She discovered that the only rival to Ailill's bull,
Finnbennach, was
Donn Cúailnge, owned by
Dáire mac Fiachna, a vassal of Conchobar's. She sent messengers to Dáire, offering wealth, land and sexual favours in return for the loan of the bull, and Dáire initially agreed. But when a drunken messenger declared that, if he had not agreed, the bull would have been taken by force, Dáire withdrew his consent, and Medb prepared for war. An army was raised including contingents from all over Ireland. One was a group of Ulster exiles led by Conchobar's estranged son
Cormac Cond Longas and his foster-father
Fergus mac Róich, former king of Ulster and one of Medb's lovers. It is reported that it took thirty men to satisfy her, or Fergus once. Medb's relationship with Fergus is alluded to in the early poem
Conailla Medb míchuru ("Medb has entered evil contracts") by
Luccreth moccu Chiara (c. 600); it asserts that Medb wrongly seduced Fergus into turning against Ulster "because he preferred the buttocks of a woman to his own people". Because of a divine curse on the Ulstermen, the invasion was opposed only by the teenage Ulster hero
Cúchulainn, who held up the army's advance by demanding single combat at fords. Medb and Ailill offered their daughter Findabair in marriage to a series of heroes as payment for fighting Cúchulainn, but all were defeated. Nevertheless, Medb secured the bull. However, after a final battle against Conchobar's assembled army, she was forced to retreat. Donn Cúailnge was brought back to Cruachan, where it fought Ailill's bull, Finnbennach, killing him, but dying of his wounds. Also, throughout the Táin Bó Cúailnge Medb has several encounters with Cúchulainn in which he kills either her pets or handmaidens and the place in which they were killed is then named after them, which illustrates the importance of landscape throughout the text of the Táin Bó Cúailnge. Examples of this occur when Cúchulainn "slung a stone and killed a pet stoat as it sat on Medb's shoulder by her neck, south of the ford. Hence the name Meithe Togmaill, Stoat Neck" and when he kills Medb's handmaid: "He slung a stone at her from the heights of Cuincu and killed her on the flat place that bears her name, Reid Locha, Locha's Level, in Cualinge". ==Later years==