In 964, Brian's older brother, Mathgamain, claimed control over the entire province of Munster by capturing the Rock of Cashel, capital of the ancient Eóganachta, the hereditary overlords or High Kings of Munster, but who in dynastic strife and with multiple assassinations had weakened themselves to the point they were now impotent. Earlier attacks from both the Uí Néill and Vikings were also factors. This situation allowed the illegitimate (from the Eóganacht perspective) but militarized Dál Cais to attempt to seize the provincial kingship. Mathgamain was never fully recognized and was opposed throughout his career in the 960s and 970s by Máel Muad mac Brain, a semi-outsider from the Cashel perspective but still a legitimate Eóganacht claimant from far south Munster.