The first “invasion” of Ireland was that of Cesair, the granddaughter of Noah, who, with all her companions, except for her husband Fintan, perished. Fintan turned himself into a salmon to avoid death in the flood and survived into the Christian era as a primary source of knowledge of the past.

Three hundred years later came Partholón, who, with his people, developed social customs that would become part of Irish tradition. The Partholonians also cleared land and fought off the simultaneously arriving Fomorians, a demonic group of one-legged, one-armed beings from under the sea. Unfortunately, the Partholonians all died of a plague. They were quickly followed by the arrival of Nemed and his four chieftans, who also cleared land and established local customs and crafts. After a long war with the Fomorians and the death of Nemed, the Nemedians came under cruel Fomorian rule. Eventually they rebelled, and after a flood, which destroyed most of both populations, the remaining few left for other lands.

Some of the Nemedians made their way to Greece, where they were enslaved. After many years, some rebelled and returned to Ireland as the Firbolg, or “bag men.”