Yesterday I mentioned N. G. Wilson’s statement that a complete copy of Diodorus Siculus existed in 1453. This led me to look again at his two books on how ancient Greek literature came to the west. These excellent volumes are Scholars of Byzantium, which discusses the fate of that literature in the Eastern Roman Empire from 400-1453; and From Byzantium to Italy, which talks about how it then got to Italy.
The statement about Diodorus is on the last page of text of the latter, p. 162, and note 4 on it, which tells us that Constantine Lascaris saw that volume in the imperial palace, PG 161:198. This is the last volume of the PG, in fact; containing material by Bessarion, George Trapezuntinus, Constantine Lascaris, Theodore of Gaza, and Andronicus Callistus.
The work by Constantine Lascaris is De scriptoribus Graecis Patria Siculis – Greek writers from Sicily – is in Latin, addressed to a renaissance ruler of Sicily, and commences on col. 195. Various writers are listed. I transcribe the whole entry on Diodorus from an unfortunately indistinct image:
9. Diodorus Siculus Argyrensis, historicus praestantissimus, qui sub Tiberio militavit. Historiam composuit libris quadraginta, quam Bibliothecam vocavit: de antiquitate Aegyptiorum, de Sicilia et aliis insulis, de bello Trojano, de gestis Alexandri et Romanorum usque ad suam artatem (?), quorum sex a Poggio Florentino traducti circumferuntur. Reliqui vix inventiuntur. Ego autem omnes ejus libros vidi in bibliotheca imperatoris C[onstantino]politani.
That’s plain enough:
9. Diodorus Siculus, of Argyra, a preeminent historian, who lived in the time of Tiberius. He composed a History in 40 books, which he called The Library: on the antiquities of the Egyptians, on Sicily and the other islands, on the Trojan war, the deeds of Alexander and the Romans, down to his own times, of which six translated by Poggio the Florentine are going around. The rest are hard to find. But I myself have seen all of his books in the imperial library in Constantinople.
We can take Lascaris at his word, I think. Constantine Lascaris was a nobleman of the empire who fled the city with others in 1454 and went to Italy. After staying in Milan and Rome he received an invitation from Ferdinand I to go to Naples, and eventually fixed himself in Messina in Sicily, where he taught Greek language and literature. His library ended up in the Escorial in Spain.
What became of this copy we do not know.