Viking raiders in 853 had first established a settlement near present Waterford.

It and all the other longphorts had been vacated in 902, the Vikings having been driven out by the native Irish.

The Vikings, led at first by Ottir Iarla (Jarl Ottar), return in 914  to conquer much of Ireland.

Ottir is particularly associated in Ireland with raiding and conquests in the province of Munster.

The Cogad Gáedel re Gallaib describes him raiding there alongside Ragnall and associates this with the Viking settlement of Cork.

Their base for this activity is Loch dá Caech or present day Waterford.

Later the same epic describes Ottir conquering the eastern part of Munster from his seat at Waterford, but it is unclear if he ruled it as king outright or was in any way subject to Ragnall, because the annals offer a different chronology.