In Norse mythology according to the Eddic poem Rígsþula, Erna was the mother of eleven sons by Jarl, the ancestors of the class of warriors in Norse society. Her father was Hersir, a tribal chief.

The Iverni (, Iouernoi) were a people of early first mentioned in Ptolemy's 2nd century Geography as living in the extreme south-west of the island. He also locates a "city" called Ivernis (, Iouernis) in their territory, and observes that this settlement has the same name as the island as a whole, Ivernia (, Iouernia). The name Iverni has been derived from Proto-Indo-European *PiHwerjoHn, "the fertile land". It was probably once the name given to all the peoples of Ireland, but by Ptolemy's time had a more restricted usage applicable to the inhabitants of the south-west. These Iverni can be identified linguistically with the Érainn (Éraind, Érnai, Érna), a people attested in Munster and elsewhere in the early Middle Ages.