William had just taken control of the Duchy when Constantinople fell to the Ottomans. As a citizen of Venice, he had himself included in the treaty between Venice and the Ottoman Empire, which provided him with a measure of protection. He also signed a treaty with Sultan Mehmed II that recognized him as Duke and to live in peace and harmony with the Porte; he also received the right to fly the flag of St. Mark in his realm. Nevertheless, eventually Sultan Mehmed pressured him into paying tribute to him, and it was only by bowing to the Sultan's demands that William was able to hold on to his realm until his death.