The Picts and Britons now recovered their independence; for Aldfrith, apparently an illegitimate son of Oswio, who succeeded, made no attempt to reconquer them.
Finally in 756, having now allied himself with Ongus king of the Picts, he successfully attacked Dumbarton (Alcluith), the chief town of the Britons of Strathclyde.
He sent an embassy to Charlemagne in 768 and was deposed in 774, whereupon he fled to Bamburgh and afterwards to the Picts.
The Catrail or Picts' Work begins near the town and passes immediatelyto the west.
He succeeded in making the majority of the Britons, Picts and Scots tributary to him.