It was at the Battle of Benevento that the "Guelph" Capetians gained the Sicilian kingdom from the "Ghibelline" Swabians, this was cemented after victory at Tagliacozzo. In keeping with the political landscape of the period, Charles is described by scholars as shrewd, energetic and highly ambitious. He signed the Treaty of Viterbo in 1267 with Baldwin II of Courtenay and William II of Villehardouin, the political alliance gave many of the rights of the Latin Empire to Charles and a marriage alliance for his daughter Beatrice of Sicily. The Byzantines had taken back the city of Constantinople in 1261 and this was a plan to take it back from Michael VIII Palaiologos. It also recognised Charles' possession of Corfu and cities in the Balkans such as Durazzo, as well as giving him suzerainty over the Principality of Achaea and sovereignty of the Aegean islands aside from those already held by the Republic of Venice. For a while Charles was preoccupied helping his French brother in the unsuccessful Eighth Crusade on Tunis. After this he once again focused on Constantinople, but his fleet was wrecked in a freak storm off the coast of Trapani. With the elevation of Pope Gregory X, there was a truce between Charles and Michael in the form of the Council of Lyons, as Christians focused on improving ecumenical relations, with hopes of regaining the Kingdom of Jerusalem back from the Muslims.