In considering his monumental work, the first portion deals with history until the destruction of Troy, the second segment with the death of Alexander, and the third, turning an eye westward, with the period leading up to Julius Caesar's conquest of Gaul. Of the forty books, volumes 1 through 5 exist, and volumes 11 through 20 (inclusive) have also been preserved. Only those texts recounting events during the author's own lifetime may be said to be truly original. It is thought that Hieronymus of Cardia and, for earlier periods, Ephorus, were the sources of his knowledge of Greek history.

Certain passages of Diodorus' "missing" books are cited by other authors, such as Photius. That Diodorus' work itself has preserved the earlier writings of several historians is important. His "mythic" treatment of Egyptian, Ethiopian, Assyrian and Persian history is relevant to studies of these civilizations. However, he did not necessarily travel to every place he wrote about. His description of Mesopotamia's legendary Babylonian rulers is probably based on those of Ctesias.

As regards Sicily, Diodorus chose to live in larger cities rather than the isolated Agyrium. His geographical observations are useful in identifying ancient communities and their relative importance. In general, his work is valuable if read critically and considered in its proper historical context. Diodorus remains the most famous Sicilian historian of the classical age.

About the Author: Palermo native Vincenzo Salerno has written biographies of several famous Sicilians, including Frederick II and Giuseppe di Lampedusa.