the coalition in 1273. However, Pope Gregory forbade Charles to attack, because he hoped to unify the Orthodox and Catholic churches with the assistance of Emperor Michael VIII. The renowned theologian Thomas Aquinas died unexpectedly near Naples on 7March 1274, before departing to attend the Second Council of Lyon. According to a popular legend, immortalised by Dante Alighieri, Charles had him poisoned, because he feared that Aquinas would make complaint against him. The historian Steven Runciman emphasises that "there is no evidence for supposing that the great doctor's death was not natural". Southern Italian churchmen at the council accused Charles of tyrannical acts. Their report reinforced the Pope's attempt to reach a compromise with Rudolf of Habsburg, who had been elected king of Germany by the prince-electors of the Holy Roman Empire. In June, the Pope acknowledged Rudolf as the lawful ruler of both Germany and Italy. Charles's sisters-in-law, Margaret and Eleanor, approached Rudolf, claiming that they had been unlawfully disinherited in favour of Charles's late wife. Michael VIII's personal envoy announced at the Council of Lyon on 6July that he had accepted the Catholic creed and papal primacy. About three weeks later, Pope Gregory again prohibited Charles from launching military actions against the Byzantine Empire. The Pope also tried to mediate a truce between Charles and Michael, but the latter chose to attack several smaller states in the Balkans, including Charles's vassals. The Byzantine fleet took control of the maritime routes between Albania and southern Italy in the late 1270s. Gregory only allowed Charles to send reinforcements to Achaea. The organisation of a new crusade to the Holy Land remained the Pope's principal object. He persuaded Charles to start negotiations with Maria of Antioch about purchasing her claim to the Kingdom of Jerusalem. The High Court of Jerusalem had already rejected her in favour of Hugh III of Cyprus, but the Pope had a low opinion of Hugh. The war with Genoa and the Lombard towns increasingly occupied Charles's attention. He appointed his nephew Robert II of Artois as his deputy in Piedmont in October 1274, but Artois could not prevent Vercelli and Alessandria from joining the Ghibelline League. The following summer, a Genoese fleet plundered Trapani and the island of Gozo. Convinced that only Rudolf I could achieve a compromise between the Guelphs and Ghibellines, the Pope urged the Lombard towns to send envoys to him. He also