failure of Hugo de Sully's expedition convinced Charles of Anjou that an invasion of the Byzantine Empire by land was not feasible, and he thus considered a naval expedition against Byzantium. He found an ally in Venice and in July 1281, the Treaty of Orvieto formalized this collaboration. Its stated purpose was the dethronement of Michael VIII in favor of the titular Latin emperor Philip of Courtenay and the forcible establishment of the Union of the Churches, bringing the Greek Orthodox Church under the authority of the Pope. Its principal motivation, however, was to re-establish the Latin Empire, under Angevin domination, and to restore Venetian commercial privileges in Constantinople. Under the terms of the treaty, Philip and Charles were to supply 8,000 troops and cavalry, and sufficient ships to transport them to Constantinople. Philip, the Doge of Venice Giovanni Dandolo, and Charles himself or Charles' son, Charles, Prince of Salerno, were to personally accompany the expedition. In practice, Charles would have supplied almost all of the troops, Philip having little or no resources of his own. The Venetians would supply forty galleys as escorts for the invasion fleet, which was to sail from Brindisi no later than April 1283. Upon Philip's restoration to the throne, he was to confirm the concessions of the Treaty of Viterbo and the privileges granted to Venice at the founding of the Latin Empire, including recognition of the Doge as dominator of "one-fourth and one-eighth of the Latin Empire." A second document was also drawn up to organize a vanguard to precede the main expedition of 1283. Charles and Philip were to supply fifteen ships and ten transports with about 300 men and horses. The Venetians were to provide fifteen warships for seven months of the year. These forces would make war against Michael VIII and "other occupiers" of the Latin Empire (presumably the Genoese), and would meet in Corfu by 1 May 1282, paving the way for the next year's invasion. The two treaties were signed by Charles and Philip on 3 July 1281, and were ratified by the Doge of Venice on 2 August 1281. Sicilian Vespers On Easter Monday 30 March 1282, in Sicily the local people began attacking French forces in an uprising which would become known as the Sicilian Vespers. The massacre went on for weeks throughout the island and they also destroyed the Angevin fleet gathered in the harbor