Sometime in the 850s or 860s the three
Viking brothers
Ímar,
Amlaíb Conung and
Auisle began to rule as
kings in Dublin. Ímar died in 873, Amlaíb in 874, and Auisle in 867; with
Bárid, son of Ímar probably succeeding them as king. Some scholars have also suggested that
Oistin, son of Amlaíb ruled with Bárid as co-king. According to some scholars
Halfdan Ragnarsson was brother to Ímar, Amlaíb Conung and Auisle, and hence uncle to Bárid and Oistin. Halfdan is not described as ruling in Ireland like his brothers in any contemporary source, but he is instead described as one of the leaders of the
Great Heathen Army which invaded the Anglo-Saxon kingdoms of England from 865 onwards. Halfdan is identified by some as a brother of the three kings of Dublin because in the
Anglo-Saxon Chronicle he is described as the brother of another leader of the Great Heathen Army named
Ívarr. This Ívarr is often considered the same as Ímar, primarily because Ímar is absent from Irish records during the period Ívarr is described as a leader of the Great Heathen Army. According to the later Norse
sagas Halfdan was the son of the legendary Viking
Ragnar Lodbrok, but the historicity of Ragnar is uncertain and the identification of Ragnar as the father of Halfdan is not to be relied upon. The main historical sources for this period are the Norse sagas and the
Irish annals. Some of the annals, such as the
Annals of Ulster are believed to be contemporary accounts, whereas the sagas were written down at dates much later than the events they describe and are considered far less reliable. A few of the annals such as the
Fragmentary Annals of Ireland and the
Annals of the Four Masters were also complied at later dates, in part from more contemporary material and in part from fragments of sagas. According to
Downham: "apart from these additions [of saga fragments], Irish chronicles are considered by scholars to be largely accurate records, albeit partisan in their presentation of events". ==Battle==