Macha is a powerful goddess having horse, sovereignty, and war associations. To the Celts the horse symbolized sovereignty over the Land and military might. The horse also tends to have associations with the fertility of the Land, a power that should always be respected. The failure of the men of Ulster to respect Macha's power causes the famed "Debility of the Ulstermen" in the Taín.

Described as beautiful AND terrible Macha has many stories associated with her. The most famous tells of why the Ulstermen are struck with an enchanted debility when Queen Maeve attacks Ulster in the Cattle Raid of Cooley.

Macha takes a mortal husband named Crunniac, just after Crunniac's mortal wife dies leaving him a widower. Macha enters Crunniac's home, starts cleaning and sees to the needs of Crunniac's children without a word. She makes love to Crunniac that night and stays.

After nearly nine months Crunniac is invited to attend a celebration at his king's Dun. He asks Macha if she will attend with him, but she refuses, warning him:

"Take care," she said. "Say nothing about me. Watch your tongue at all times."

Crunniac attends the feast and looses himself in drink, loosening his tongue. A horse race is about to begin, with the king's own chariot horses in the running. Crunniac hears the king boasting that his horses are faster than any in the world. Crunniac drunkenly jokes that even his wife could run faster than the king's horses. The king is outraged and sends for Macha to run against his horses and prove her husband right. If she cannot win the race Crunniac will be put to death.

Macha is escorted to the Dun whereupon the king angrily demands that she run against his horses. Macha replies:

"As you can see, my lord, I am near to term. I cannot run. If you will wait a month or two I will make good on my husband's boast."

The king refuses her fair offer and demands that she run the race now. Macha then turns to the crowd behind her and asks if any will defend her cause, and no one does. With no one to defend her, Macha reluctantly took her place at the starting line. At the shout of the king the race was begun. Despite her pregnancy Macha won the race. While crossing the finish line, however, she gaves birth to twins, a boy and a girl.

Furious she pronounces a curse on the men of Ulster saying:

"Men of Ulster, you have shown me no mercy even in the weakness of childbirth. You will suffer the same pain and weakness for five days and four nights whenever you most need your strength - you and your sons and your son's sons until the ninth generation!"