On May 29th 1453 the city of Constantinople fell to the Ottoman Turks to be renamed Istanbul. For 800 years Constantinople protected Europe from Islamic invaders and preserved Greek and Christian civilization. After the fall, Byzantine scholars fled to Italy bearing the mustard seed of Western Civilization and inaugurated the Renaissance.
The Turks had some help from the Venetians. Conquerors exploit decadence and treachery. "The Christian land, has lost his sword and shields." Mehmed II