Tuatha Dé Danann
In many Gaelic tales, the "aos sí" are later, literary versions of the Tuatha Dé Danann ("People of the Goddess Danu")—the deities and deified ancestors of Irish mythology. Some sources describe them as the survivors of the Tuatha Dé Danann who retreated into the Otherworld when fleeing the mortal Sons of Míl Espáine who, like many other early invaders of Ireland, came from Iberia. As part of the terms of their surrender to the Milesians, the Tuatha Dé Danann agreed to retreat and dwell underground. (In later interpretations, each tribe of the Tuatha Dé Danann was given its own mound.) Geoffrey Keating, an Irish historian of the early 17th century, equates Iberia with the Land of the Dead, providing a possible connection to the "aos sí."