In the spring of the next year, 1688, a well equipped army was sent to the Hungarian frontier, in the hope of retrieving the defeats of the past five years. The Austrians, however, had made good use of the interval. They had now three armies in the field, under the command of Prince Charles of Lorraine, Prince Louis of Baden, and Prince Eugène of Savoy—all three generals of exceptional ability. They invested the fortress of Erlau and captured it. The road to Belgrade now lay open to them. This supremely important city, the bulwark to the Balkans and the gateway to Hungary, was treacherously surrendered by its garrison in August 1688 after a bombardment of only twenty-one days. Prince Louis of Baden about the same time invaded Bosnia and occupied a great part of it. Dalmatia revolted and threw over Turkish rule. Nisch was later occupied by the Austrians, and Widdin, on the Danube, fell into their hands. By 1689 the only fortresses in Hungary remaining to the Turks were Temesvar and Warardin. Farther eastward the Turks had been more fortunate. An army of Tartars from the Crimea overran Poland in 1688 and defeated a Polish army on the Sereth. In the following year, when Russia joined in the combination against the Ottomans and sent an army into the Crimea, it met with a severe defeat. These were the only rays of light to the Turks. Elsewhere they met with a succession of disasters. The Balkan provinces, for the first time since the days of Hunyadi, were threatened by the Austrians. Parts of Bosnia and Serbia were in their hands. The whole of Greece and Albania had been conquered by the Venetians, under Morosini, and the Turkish fleets had been swept off the Mediterranean by the combined fleets of Venice, the Pope, the Knights of Malta, and the Duke of Tuscany. On the Ottoman side no single general of any capacity had appeared. It was under these conditions that a general council of the Empire was summoned at Adrianople at the end of 1689. After a long discussion, it advised the Sultan to appoint as Grand Vizier Zadé Kiuprili, who had been passed over by Sultan Mahomet IV in favour of the corrupt and incompetent Kara Mustapha after the death of Ahmed Kiuprili. After thirteen years of misgovernment and calamity this third member of the Kiuprili family was called to power. He showed at once great vigour and capacity. Addressing the chief dignitaries of the Empire, he described the perilous condition of affairs: “If we go on as we have been in the past, another campaign will see the enemy encamped before Constantinople.” He took immediate steps to restore the financial position.