Run of Alt Clut

Rhun ab Arthgal
King of Strathclyde
Rhun's title as it appears on folio 29r of Paris Bibliothèque Nationale MS Latin 4126 (the Poppleton manuscript): "regis Britannorum" ("king of the Britons")
Predecessor	Arthgal ap Dyfnwal
Issue	Eochaid
Father	Arthgal ap Dyfnwal

Rhun ab Arthgal was a ninth-century King of Strathclyde. He is the only known son of Arthgal ap Dyfnwal, King of Alt Clut. In 870, during the latter's reign, the fortress of Alt Clut was captured by Vikings, after which the Arthgal and his family may have been amongst the mass of prisoners taken back to Ireland. Two years later Arthgal is recorded to have been slain at the behest of Causantín mac Cináeda, King of the Picts. The circumstances surrounding this regicide are unknown. The fact that Rhun seems to have been Causantín's brother-in-law could account for Causantín's interference in the kingship of Alt Clut.

The Viking's destruction of the capital fortress of the Kingdom of Alt Clut appears to have brought about a reorientation of the kingdom towards the valley of the River Clyde. In consequence, the realm came to be known as the Kingdom of Strathclyde. Either Rhun or his father could have been the first kings of Strathclyde. In the years following the fall of Alt Clut, Rhun's realm may have endured periods of Pictish and Viking overlordship. Despite his kinship with the Pictish king, there is reason to suspect that the two clashed at some point.

It is unknown when Rhun's reign came to an end or when he died. One possibility is that he fell with Causantín, who seems to have been killed warring against the Vikings in 876. Certainly, Rhun's son, Eochaid, is recorded to have succeeded Causantín's successor, Áed mac Cináeda, King of the Picts, after 878. Whether Eochaid's succession reflects the end of Eochaid's reign and life is unknown.

Rhun's patrilineal ancestry is evidenced by a pedigree preserved within a collection of tenth-century Welsh genealogical material known as the Harleian genealogies. According to this source, Rhun was a son of Arthgal ap Dyfnwal, King of Alt Clut (died 872), and descended from a long line of kings of Alt Clut. Rhun is Arthgal's only known son.