Most beliefs about nature and man, which were not founded on scientific observation, have served directly or indirectly religious and social interest… - J. B. Bury

Polybius is not less express than Thucydides in asserting the principle that accurate representation of facts was the fundamental duty of the historian. He lays down that three things are requisite for performing such a task as his: the study and criticism of sources; autopsy, that is, personal knowledge of lands and places; and thirdly, political experience.

Not long after his (Justinian) accession, he reaffirmed the penalties which previous Emperors had enacted against the pagans, and forbade all donations or legacies for the purpose of maintaining "Hellenic impiety,"...by making the profession of (Christian) orthodoxy a necessary condition for public teaching Justinian accelerated the extinction of "Hellenism." ... This event had a curious sequel. Some of the philosophers whose occupation was gone resolved to cast the dust of the Christian Empire from their feet and migrate.

Writing the history of the present is always a very different thing from writing the history of the distant past. The history of the distant past depends entirely on literary and documentary sources; the history of the present always involves unwritten material as well as documents. But the difference was much greater in the days of Thucydides than it is now.