The Ulster Cycle
The Ulster Cycle was told in two places: the eleventh century Book of the Dun Cow, and the fourteenth century Yellow Book of Lecan. The Ulster Cycle chronicles the adventures of a succession of great heroes, most notably Cuchulainn, a warrior of tremendous stature and ferocity. The cycle begins with the tale of Fergus, an impossibly gigantic king of Ulster. Fergus wishes to marry Nessa, his brother's widow, who will only consent if Fergus will make her young son king. Fergus, all too glad to be rid of the responsibility, readily agrees, and seven-year-old Connor becomes king of Ulster.
Macha, one of the older Celtic goddesses, was often portrayed as a horse. She is sometimes seen as an attribute of the Morrigan, a triplicate goddess of fertility, war, and death. It was to Macha that the heads of the battle-dead belonged.
Despite King Connor's youth, all goes well under his reign until one terrible incident. A wealthy cattleman by the name of Cruinniuc boasts that his wife Macha, a swift runner, can outrace the king's chariots. Despite her protests, the king forces the heavily pregnant Macha to compete. She wins the race, but the exertion proves too much. After giving birth to twin babies, she expires at the finish line, cursing the insensitive men of Ulster to suffer a woman's labor pains whenever the kingdom is under threat. Macha's curse carries down nine generations of Ulster men, until the birth of the semi-divine hero Cuchulainn.
The Cattle Raid of Cooley
The central tale of the Ulster Cycle is known as the Cattle Raid of Cooley, which tells the tales of two magical bulls. These are Donn Cuailnge, the brown bull of Cooley, and Finnbennach, the white-horned bull of Ai. The white-horned bull belongs to the wealthy, powerful, and exceedingly avaricious Queen Medb (Maeve), whose enormous greed cannot be satisfied. Medb wishes to humiliate her ineffectual husband and desires to add the brown bull to her already prodigious wealth. Upon hearing of the mysterious affliction of the Ulster men, she sets off with her armies to seize the great bull.
Medb's armies are not aware of the existence of Cuchulainn, however, and soon meet with furious resistance. Clever Cuchulainn invokes the ancient right of single combat and staves off Medb's army for months, slaying every champion the queen sends to meet him.
The brown and white bulls of the Cooley saga are no ordinary bulls, of course, but the result of a magical battle between two enchanted shape-changers, a pair of foolish magicians whose end comes in a most fitting way.
Cuchulainn's distractions are successful, and the men of Ulster, recovered from their labor pains, are able to easily defeat Medb's depleted forces.
But Queen Medb is clever. She succeeds in stealing the bull anyway, while the men are distracted by the battles. In the end, all the fighting is to no avail. The two bulls, having picked up an old disagreement, soon commence battling between themselves over which is superior. The battle between the bulls rages all night and ranges the breadth of Ireland, until at last the white-horned bull Finnbennach lies dead. The brown bull, now bored, breaks free and returns to his home in Ulster, where he too expires from his exertions.
Medb, of course, is not finished with Cuchulainn, and seeks her revenge on him through more trickery. Cuchulainn, like most Celtic heroes, is under a geas, a magical proscription which becomes a curse if broken. Cuchulainn's geas is that he must accept any meal offered him but he must never eat dog's meat. When the geas is discovered, Medb's simple solution is to offer the hero a meal of dog's meat. Spiritually broken, Cuchulainn is easily defeated, felled by the spear of Lugaid.