While the French armies in Italy and Switzerland tried to preserve the Sister Republics, Bonaparte pursued his own campaign in Egypt. He explained in a letter to the Directory that Egyptian venture was just the beginning of a broader campaign "to create a formidable diversion in the campaign of Republican France versus monarchic Europe. Egypt would be the base of something much larger than the original project, and at the same time a lever which will aid in the creation of a general uprising of the Muslim world." This uprising, he believed, would lead to the collapse of British power from the Middle East to India. With this goal in mind, he left Cairo and marched his army across the Sinai desert into Syria, where he laid siege to the port of Saint-Jean-d'Acre of the Ottoman Empire, which was defended by a local army and supplied by a British fleet offshore. His long siege and attempts to storm the city were a failure; his army was ravaged by disease, it was down to 11,000 men, and he learned that an Ottoman army was to be embarked by the British fleet to sail to Cairo to recapture the city. On 17 May, he abandoned the siege and was back in Cairo by 4 June. The British fleet landed the Ottoman army, but as soon as they were ashore they were decisively defeated by Bonaparte at the Battle of Aboukir on 25 July 1799.