The capture of Constantinople (1453) by the Ottoman troops of Mehmed II was a historical turning point. The political reference point of Eastern Christianity was now in Muslim hands, the Ottomans representing in the eyes of late medieval Europeans not only an enemy of the true faith, and as such an obstacle for ecclesiastical unity, but also a potential rival of the papacy as a political power. In short, within the contemporary context and the socially dominant apocalyptic frame of mind, the Ottomans were viewed as an existential threat for Christianity as a whole. While the papal reaction to this development was to go on the offensive, expressed through the call for a new crusade, the emergence of a few voices expressing divergent theological content and political orientation had special significance. One of the voices which ‘set off the politics of religious synthesis from different quarters” was that of George of Trebizond (1395–1472/3), a Cretan emigrant to Italy who lived in Venice and Florence before moving to Rome. He had converted to Catholicism without losing his sense of belonging to the East, and became a prominent figure of the Italian intellectual elite and an editor of classical and theological literature, as well as a member of the Vatican bureaucracy.