The article presents the efforts of Pope Pius II (1458-1464) to build a military coalition of Christian nations against the Ottoman Empire. For the humanist pope Pius II standing up to Turkey was not just a option dependent on changing perceptions of Rome's interests and European politics. He believed that the Ottoman expansion was a threat that had to be tackled head on if the flowering Italian humanism and the whole of Western civilisation was to survive. Consequently, he called on all Christian nations to unite against islam and organized a crusading congress in Mantua in 1459. When it became clear that the European powers were less than eager to fall in with his plans, Pius II may have contemplated opening a direct line of communication with the Sultan. In a letter, or rather a small tract, intended to persuade Mehmed II to embrace the Christian faith he suggested that it would make him the most powerful ruler in the world. Pius II pointed to the example of the Grand Duke of Lithuania Władysław Jagiełło, whose conversion to Christianity enabled him to become king of Poland. It seems, however, that the letter was never dispatched to the Porte; in fact, as some historians suggest, it might have been written to catch the attention of the numerous home-grown Turkophiles and cause some ripples on the Christian side of the great frontline.