This is the Irish Iliad. Medb (Maeve), the warrior queen of Connaught, disputes with her husband, Ailill, over their respective wealth. Because possession of the white-horned bull guarantees Ailill's superiority, Medb resolves to secure the even-more-famous brown bull of Cooley from the Ulstermen.
Irish Mythology - Mythical Cycle - Book of Invasions