Roger spent most of the decade beginning with his coronation and ending with his great Assizes of Ariano fending off one invader or other and quelling rebellions by his premier vassals: Grimoald of Bari, Robert of Capua, Ranulf of Alife, Sergius of Naples, et al. In 1139, by the Treaty of Mignano, Roger received the recognition of his kingship from the legitimate pope. It was through his admiral George of Antioch that Roger then proceeded to conquer the Mahdia in Africa, taking the unofficial title "king of Africa".