Arthgal ap Dyfnwal

Arthgal ap Dyfnwal
King of Alt Clut
Arthgal's title as it appears on folio 25v of Oxford Bodleian Library MS Rawlinson B 489 (the Annals of Ulster).
Reign	×872
Predecessor	Dyfnwal ap Rhydderch
Successor	Rhun ab Arthgal
Died	872
Father	Dyfnwal ap Rhydderch

Arthgal ap Dyfnwal (died 872) was a ninth-century King of Alt Clut. He descended from a long line of rulers of the British Kingdom of Alt Clut. Either he or his father, Dyfnwal ap Rhydderch, King of Alt Clut, may have reigned when the Britons are recorded to have burned Pictish ecclesiastical site of Dunblane in 849.

In 870, the seat of Arthgal's realm—the island fortress of Alt Clut—was besieged by the Viking kings Amlaíb and Ímar. After four months, the fortress fell to the Vikings, who are recorded to have transported a vast prey of British, Pictish, and English captives back to Ireland. The fall of Alt Clut marked a watershed in the history of Arthgal's realm. Afterwards, the capital of the kingdom appears to have relocated up the River Clyde to the vicinity of Govan and Partick, and became known as the Kingdom of Strathclyde.

Two years after the fall of Alt Clut, Arthgal is recorded to have been assassinated at the behest of Causantín mac Cináeda, King of the Picts. The circumstances surrounding Arthgal's death or uncertain. Whilst it is possible he was captured by the Vikings in 870 and slain whilst still in captivity, it is also possible that he was reigning as king when he died. The fact that Arthgal's succeeding son, Rhun, was Causantín's brother-in-law could be evidence that Arthgal was killed to make way for Rhun. Another possibility is that, following the destruction of Alt Clut, Arthgal ruled as a puppet king under Vikings. If so, this could also account for Causantín's actions. On the other hand, Causantín may have merely acted out of sheer opportunism, and Rhun may have succeeded to the throne without his assistance. In any event, either Arthgal or Rhun could have been the first kings to rule as King of Strathclyde.