The dating of Philo’s works is dependent on one’s understanding of his life and work. If he were active in political functions and offices during most of his adult life it is not only possible but rather plausible that his work as an author and expositor of the Scriptures must have found place during a rather long period.
It is, alas, not possible to fit all his writings into a chronological scheme. The Legatione and Flaccum must, however, have been written after the events they inform us of, i.e., after 38 CE. Perhaps De Animalibus was written at the same time. We cannot place all his philosophical writings in the period of his younger age and the exegetical in the later. If De Animalibus, however, belongs to his later years it shows that his philosophical interest was very intact at that time. On the other hand, it is scarcely reasonable to place all his writings in his later years.
There is thus one date that must have been crucial for Philo, and that is the uprisings and the progrom-like persecutions of the Jews in Alexandria in 38f CE. How did these influence Philo’s life and work?
Here I find Michael F. mach’s suggestions challenging:
The well educated formerly wealthy member of the Jewish community finds himself driven out of the centre of Hellenistic learning in his home-town and seems to withdraw into the synagogue. Here he encounters Jews who had not yet become part of the broader Hellenistic philosophical culture. On the one hand he eagerly tries to make use of his acquired skills, he will even attempt to show how much Hellenistic philosophy and the teaching of Moses are basically one and the same; on the other hand he must reconsider his enthusiasm for the Greek culture from the position of a rejected outsider. Somewhat between these two points one may locate Philo’s longing for a better understanding of the high Jewish culture in the eyes of his former companions. This whole process takes place during years of ongoing social and political troubles (which have a direct impact on his and his family’s economic situation) ending in open riots and armed hostility. (Mach, Michael F., ‘Choices for Changing Frontiers: The Apologetics of Philo of Alexandria,’ In Yossef Schwartz and Volkhard Krech (Eds.), Religious Apologetics – Philosophical Argumentation. . Religion in Philosophy and Theology 10. Tübingen: J. C. B. Mohr (Siebeck), 2003), pp. 319-333. here p. 326.
The Legatione and Flaccum at least must have been written after this events, and these events are probably also pivotal in his changed attitude to the Romans and his more direct political agenda in these two works.
The challenging issue in Mach’s statement above, however, is that he also suggest a more far-reaching effect of these events in 38 and the immediate following years.