 There was a merger of the Gaelic and Pictish crowns, although historians continue to debate whether it was a Pictish takeover of Dál Riata, or the other way around.This culminated in the rise of Cínaed mac Ailpín in the 840s, who brought to power the House of Alpin who were leaders of a combined Gaelic-Pictish kingdom for almost two centuries.In 870 Dumbarton was besieged by Amlaíb Conung and Ímar, "the two kings of the Northmen", who "returned to Dublin from Britain" the following year with numerous captives.