The Milesians or sons of Míl are the final race to settle in Ireland, according to the Lebor Gabála Érenn, a medieval Irish Christian history. The Milesians represent the Irish people. They are Gaels who sail to Ireland from Iberia (Hispania) after spending hundreds of years travelling the Earth. When they land in Ireland, they contend with the Tuatha Dé Danann, who represent the Irish pantheon of gods. The two groups agree to divide Ireland between them: the Milesians take the world above, while the Tuath Dé take the world below (i.e. the Otherworld).
Scholars believe that the tale is mostly an invention of medieval Christian writers.[1][2]