The final pre-Christian invasion of Ireland was that of the Gaels, the Celts who had long ago fled Ireland for Spain and now returned as the Milesians, the “Sons of Mil,” that is, Mil of Spain. A leader of this invasion was the druidic poet-prophet and warrior Amairgen, who uses his powers to push aside the clouds created by the Tuatha to hinder their arrival. Amairgen contains all the elements of creation within his druidic self. “The sea’s wind am I,” he sings, and with his song Celtic Ireland is born. Moving toward Tara, the Milesians meet the triune queens, Banba, Fotla, and Eriu, whose names will be associated with Ireland forever. The three kings at Tara work out a truce with the Milesians. The Milesians will retreat to the sea and “invade” again. The Tuatha send a powerful wind to keep the Milesians at sea, but Amairgen’s power is stronger, and the wind is brushed aside, leaving the Milesians free to land and to defeat the Tuatha. In the peace agreement, the Milesians take control of the world above ground and the Tuatha are confined to the land below. The Tuatha remain in sidh, underground mounds, and have been referred to ever since as the sidh, the “fairies,” or “Little People.”

Ireland was now ready for the deeds of the early kings and for the heroic events that characterize the mythological sagas of the country.