Lugh's Sling Stone and Balor's Eye

The armies met at Mag Tuired, and the battle is remembered in the surviving text as a contest of matched champions and magical resource as much as of open combat: the physician Dian Cecht and his children tended the Tuatha De Danann's wounded at a healing well that returned fallen warriors to the fight, while the Fomorian smiths worked to keep pace with Tuatha De Danann weapons. Balor, the Fomorian giant, carried a single baleful eye whose lid took several men to lift and which killed or withered whatever it looked upon, a weapon turned against his own people in earlier tellings before being wielded at Mag Tuired itself.

Lugh, despite instructions to stay out of the fighting because of his value as craftsman and leader rather than combatant, entered the battle as Balor's eye was being uncovered and struck it with a stone from his sling, driving the eye out through the back of Balor's head so that its gaze fell instead on the Fomorian ranks behind him. Balor's death broke the Fomorian line, and the Tuatha De Danann's victory ended Fomorian domination of Ireland and confirmed Lugh, rather than the restored Nuada, as the people's effective leader for the remainder of the tale. The tale belongs to Ireland's Mythological Cycle and makes no claim to historical event; Moytirra, the plain in County Sligo, is a real place onto which the legendary battle was mapped.