, the brother-in-law of Arthgal's son, and the man who instigated Arthgal's death, as it appears on folio 29v of Paris Bibliothèque Nationale Latin 4126 (the
Poppleton manuscript): "''''". Arthgal died in 872. The
Annals of Ulster and
Chronicon Scotorum reveal that he was slain at the behest of
Causantín mac Cináeda, King of the Picts.
Rhun, Arthgal's only known son, is the last king to be listed in the Harleian pedigree that pertains to Arthgal. If Rhun succeeded Arthgal—as seems likely—it is uncertain how long he outlived him. Despite Causantín's part in Arthgal's demise, Rhun is otherwise known to have married a sister of Causantín at some point. Although the circumstances surrounding Arthgal's assassination are unknown, the familial relationship between Causantín and Rhun could be evidence that Arthgal's demise was orchestrated to allow Rhun gain the throne. One possibility is that Rhun had been exiled from his father's realm, and had been living at the Pictish royal court when Amlaíb and Ímar commenced their campaign. This could mean that Causantín acted to offset any rival Rhun had in regard to the British kingship. Conversely, if there was no strife between Rhun and Arthgal, Causantín's actions against the latter could have been carried out in the context of an intrusive and aggressive neighbour. This monument is perhaps the finest example of the so-called 'Govan School' of sculpture. The sarcophagus could to be that of Arthgal's adversary, Causantín. Arthgal's elimination may have been carried out in the context of an attempt by Causantín to capitalise upon the political turmoil wrought by the Viking onslaught. The destruction of Alt Clut marks the last time the fortress appears on record until the thirteenth century. Although the site could have served as a Viking military base following the British defeat, there is no archaeological evidence evincing its use as a seat of lordship until later centuries. Perhaps the site was discredited, and came to be regarded as unsuitable to the ruling dynasty thereafter. Certainly, the British capital appears to have shifted up the
River Clyde to the vicinity of
Govan and
Partick. Whilst the former site—on the north bank of the River Clyde—appears to have been utilised by Arthgal's eighth-century predecessors, the latter site—on the south bank—could well have been used at least a century earlier. at
Govan. The scene shows a now-nonexistent artificial hill that could to have been the royal assembly site of the
Kingdom of Strathclyde following the fall of Alt Clut. This relocation of the capital seems to be borne out by surviving documentary sources. Until the fall of Alt Clut, for example, the rulers of the realm were styled after the fortress. After the loss of this site, the Kingdom of Alt Clut came to be known as the
Kingdom of Strathclyde in consequence of its reorientation towards Ystrat Clut (Strathclyde), the valley of the River Clyde. Arthgal himself is styled King of the Strathclyde Britons upon his death in 872—the first use of this terminology by Irish sources. Whilst it is possible that Arthgal met his end in Ireland at the hands of his Viking captors, the title accorded to him on his death could be evidence that he had instead been ruling the new Kingdom of Strathclyde. In fact, it is possible that he or Rhun was the first monarch to rule this realm. There is also reason to suspect that Arthgal's death occurred in the context of conflict with the Picts. For example, the twelfth-century
Prophecy of Berchán attributes four victories to Causantín, with the fourth described as that of ''''—a location possibly identical to
Glasgow—where he overcame the "king of the Britons of the green mantles". This source, coupled with Arthgal's obituaries, could indicate that Causantín had Arthgal executed or assassinated after defeating him in battle. Such an event may account for the specific records of Causantín's role in Arthgal's demise. Another possibility is that, following the conquest of Alt Clut, Arthgal ruled as a
puppet king under Amlaíb and Ímar. Certainly, the Vikings utilised royal puppets in the conquered English kingdoms of
Northumbria and
East Anglia. A similar relationship between Arthgal and Viking power could explain Causantín's role in Arthgal's demise, and could explain how Rhun succeeded to the throne. There is also reason to suspect that, as a result of Rhun's assumption of power, Causantín gained overlordship over the kingdom. In any event, Arthgal's apparent elimination at Causantín's instigation would appear to have rid the Picts of a neighbouring adversary, and would have served to increase Causantín's authority and reputation. ==Ancestry==