and this was cruelly suppressed by Köprülü Mehmed Pasha with the help of Janissary troops. The Greek Orthodox Patriarch of Constantinople was proven to be in treasonous contacts with the enemies of Ottoman state and Köprülü Mehmed Pasha approved of his execution. Rivals and unfriendly religious leaders were banished or executed. The support of the Janissaries was obtained once he was secure in his office. Köprülü centralized power in the empire, reviving traditional Ottoman methods of governing. He ordered those who were suspected of abusing their positions or who proved to be corrupt to be removed or executed. Those who failed at their tasks were punished severely, and unsuccessful military commanders often paid the supreme price. When Grand Admiral Topal Mehmed Pasha failed to break the Venetian blockade of the Dardanelles on 17 July 1657, Köprülü executed him and his principal officers on the spot. When rivals complained to Mehmed IV about the Grand Vizier's methods, Köprülü resigned, complaining that the Sultan had violated their agreement. Mehmed immediately asked Köprülü to return as Grand Vizier, because his methods showed such success at restoring Ottoman power. War with Venice Since the resurgence of the Republic of Venice was the immediate crisis that had prompted Köprülü's appointment as grand vizier, it was important that he demonstrate his effectiveness as a leader against the Venetians. He started on a military expeditions against the Venetian blockade of Dardanelles Straits. The Ottoman navy had a victory against Venice in the Battle of the Dardanelles on 19 July 1657. This allowed Ottomans to regain some of the Aegean islands, including Bozcaada and Limni (15 November) and to open the sea-supply routes to the Ottoman Army still conducting the sieges of Crete. War with Transylvania and the Habsburgs In 1658 he conducted a successful campaign in Transylvania. In Transylvania, Prince George II Rákóczi renounced his erstwhile allegiance to the sultan. He attempted to make his state into a major power, allying himself with other Protestant princes in an attempt to conquer Hungary and Poland. While Rákóczi invaded Poland in 1657, however, Köprülü sent the Crimean Tatars to attack Transylvania. They forced Rákóczi to retreat from Poland, but he refused to resume his obedience to the sultan. In response, in 1658, Köprülü himself led a large Ottoman army into Transylvania. This force defeated Rákóczi and forced him to flee to Habsburg lands. War with Habsburgs continued, but Ottoman