Стратклайд
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.