The Leabhar Gabhala is the book of the invasions of Ireland (Eire) and is the oldest written testimony of Celtic mythology. (1)

In it he refers to Milé, son of Breoghan, born in the "other land" across the sea, who came to Eire from "the land of death" under the command of the Gaels (Goidelic Celts).

Milé thus founded, by conquering the island, the seed of the culture that has survived to this day. Legend tells us that Galicia could be the cradle of the Celtic cultures of Ireland and Scotland, with thousands of years of history dating back to magical and mythical times.
A half-real, half-legend character who is credited with founding the city of Brigantia, which some historians identify with A Coruña and others with Betanzos.
The story goes that Breogán was a powerful king of the Celts who ruled in Brigantia, on whose coast he had a tower or lighthouse rebuilt that bears his name.