When in 1786 and 1787 at Lausanne, Switzerland, Edward Gibbon was composing the sixth and final volume of 1he History of the Decline and Fall of the Roman Empire, he had at his disposal for the famous chapter on the Ottoman conquest of Constantinople in 1453 a mere handful of sources. For the core of his narrative he drew upon three Greek works: Doukas' Turko-Byzantine History; Laonikos Chalkondylas' Turkish History; the larger of the two chronicles ascribed to the man now usually referred to as George Sphrantzes (Gibbon's Phranza); and upon the letter composed in Latin and addressed to Pope Nicholas V by Leonard of Chios, Latin archbishop of Mytilene on Lesbos, like Sphrantzes (and unlike Doukas and Chalkondylas) an established eyewitness to the siege. Not as yet available were two works that in the next century would come to enrich and refine the source material on Constantinople's fall. Of these, the first to be discovered was the diary (in Italian) of the Venetian ship's doctor, Nicolo Barbaro, an eyewitness to whom are owed precise dates for the course of the siege's events, the chronological framework to which the notices of the other sources must nowadays be fitted. The original manuscript of the Giornale, kept among the papers of the Barbaro family till 1829, came into the possession of the Biblioteca Marciana in Venice in 1837. It was edited by Enrico Comet and published in Vienna in 1856.