Philo not only represents a widespread tendency during the Roman Empire, but probably well illustrates the influence of that tendency upon later times. His numerous works were apparently much consulted by the church fathers, and thereby exerted a strong influence upon the Middle Ages. It is needless to enlarge upon the prominence of allegorical interpretation in the works of mediæval ecclesiastical writers. The conception of knowledge as esoteric was also prevalent then, though perhaps to a less extent. To give an early instance from patristic literature, Clement of Alexandria, in his _Stromata_, insists upon the necessity of veiling divine truth in allegories, and has a long discussion in favor of mysticism in learning, citing as examples Greek philosophers as well as Hebrew writers.[164] Moreover, to Philo as source we may trace back the disquisitions upon the mystic, if not magic, properties of six and other numbers which we find in Augustine[165] and apparently in almost every mediæval writer who had occasion to speak of the six days of creation and of the seventh day of rest. III. _Seneca’s Problems of Nature and divination._—We shall next consider the _Problems of Nature_—or _Natural Questions_, if one prefers merely to transcribe the Latin—of Seneca, who was practically a contemporary of Pliny. Seneca impresses one as a favorable representative of ancient science. He tells us that already in his youth he had written a treatise on earthquakes and their causes.[166] His aim is to inquire into the natural causes of phenomena; he wants to know why things are so. He is aware that his own age has only entered the vestibule of the knowledge of natural phenomena and forces, that it has but just begun to know five of the many stars, that “there will come a time when our descendants will wonder that we were ignorant of matters so evident.”[167] One must admit, however, that along with Seneca’s consciousness of the very imperfect knowledge of his own age there goes a tendency to esotericism. The following language would come fittingly from the mouth of a magician: There are sacred things which are not revealed all at once. Eleusis reserves sights for those who revisit her. Nature does not disclose her mysteries in a moment. We think ourselves initiated; we stand but at her portal. Those secrets open not promiscuously nor to every comer. They are remote of access, enshrined in the inner sanctuary.[168] Seneca seems to regard scientific research as a sort of religious exercise. His enthusiasm in the study of natural forces appears largely due to the fact that he believes them to be of a sublime and divine character, and above the petty affairs of men.