obstinate monarch. The consolidation of Charles's power in northern Italy also alarmed Clement. To appease the Pope, Charles resigned his senatorship in May 1267. His successors, Conrad Monaldeschi and Luca Savelli, demanded the re-payment of the money that Charles and the Pope had borrowed from the Romans. Victories by the Ghibellines, the imperial family's supporters, forced the Pope to ask Charles to send his troops to Tuscany. Charles's troops ousted the Ghibellines from Florence in April 1267. After being elected the Podestà (ruler) of Florence and Lucca for seven years, Charles hurried to Tuscany. Charles's expansionism along the Papal States's borders alarmed Pope Clement and he decided to change the direction of Charles's ambitions. The Pope summoned him to Viterbo, forcing him to promise that he would abandon all claims to Tuscany in three years. He persuaded Charles to conclude agreements with William of Villehardouin, Prince of Achaea, and the titular Latin Emperor Baldwin II in late May. According to the first treaty, Villehardouin acknowledged Charles's suzerainty and made Charles's younger son, Philip, his heir, also stipulating that Charles would inherit Achaea if Philip died childless. Baldwin confirmed the first agreement and renounced his claims to suzerainty over his vassals in favour of Charles. Charles pledged that he would assist Baldwin in recapturing Constantinople from the Byzantine emperor, Michael VIII Palaiologos, in exchange for one third of the conquered lands. Charles returned to Tuscany and laid siege to the fortress of Poggibonsi, but it did not fall until the end of November. Manfred's staunchest supporters had meanwhile fled to Bavaria to attempt to persuade Conrad IV's 15-year-old son Conradin to assert his hereditary right to the Kingdom of Sicily. After Conradin accepted their proposal, Manfred's former vicar in Sicily, Conrad Capece, returned to the island and stirred up a revolt. At Capece's request Muhammad I al-Mustansir, the Hafsid caliph of Tunis, allowed Manfred's former ally, Frederick of Castile, to invade Sicily from North Africa. Frederick's brother, Henrywho had been elected senator of Romealso offered support to Conradin. Henry had been Charles's friend, but Charles had failed to repay a loan to him. Conradin left Bavaria in September 1267. His supporters' revolt was spreading from Sicily to Calabria; the Saracens of Lucera also rose up. Pope Clement urged Charles to return to the Regno, but he continued his campaign in Tuscany until March 1268, when he met with the Pope. In