In the mid-sixteenth century Francois I ruled France, and Suleyman the Magnificent sat on the throne of the Ottoman Empire. Although the two leaders were separated by culture, religion and politics, the Catholic Francois and the Muslim Suleyman joined forces for a time in a political alliance to check the Hapsburg threat to both their empires. In 1544 Pierre Gilles of Albi, an established scholar and author, arrived in Constantinople as a member of a French embassy aimed at furthering this alliance. Constantinople was then the largest and wealthiest city in Europe. Its nearly 700,000 inhabitants outnumbered the combined populations of western cities such as Venice, Palermo, Messina, Catania and Naples. It was the Mediterranean capital, and home to a truly international population of Turks, Greeks, Jews, Armenians, Gypsies, Arabs, Africans, Slavs, French and others who lived side by side, for the most part in peace. They worshipped in over 400 mosques and dozens of Christian churches,...