Which battle saw the Tuatha Dé Danann defeat the Fomorians?

The Tuatha Dé Danann defeated the Fomorians in the Second Battle of Mag Tuired. Also called Cath Tánaiste Maige Tuired or the Last Battle of Mag Tuired, it is one of the central war stories of Ireland’s Mythological Cycle.

The conflict follows the oppressive rule of Bres, a king with both Tuatha Dé Danann and Fomorian ancestry. After Bres is deposed, he seeks help from the Fomorian leaders Balor and Elatha. The Tuatha Dé Danann prepare under Lugh, another figure connected to both peoples. During the battle, the Fomorian king Balor kills Nuada with his deadly eye, but Lugh defeats Balor by striking the eye with a sling-stone and turning its destructive power against the Fomorian army.

The First Battle of Mag Tuired is a different event: it was fought against the Fir Bolg, not the Fomorians. The two battles are linked in the tradition and share the same name because Mag Tuired refers to two locations in Connacht. The surviving battle narrative was compiled in the medieval period from older material.