It was supremely fortunate, both for Greece of the classical age and for all European civilization thereafter, that the conquerors of Greece were not also destroyers. What the effect would have been of Persian conquest in the early fifth century B.C. can only be conjectured; but if really effective, it could not have failed to be terribly damaging to the culture of the succeeding century. The subjugation of Greece by Macedonia, on the other hand, though perhaps in various indirect ways it diminished the vitality of Greek life, was not directly harmful to Greek literary or philosophical development. In particular the Athenian schools of philosophy flourished. Epicurus and Zeno, dominated as they both were by the problem of individual happiness, may seem to have been limited in their intellectual interests, and almost defeatist in their general attitude to life, by comparison with the far more energetic thinking of Plato and Aristotle. Even so, they were powerful figures in their own right, and in the changed conditions of the time their schools survived more vigorously than the post-Platonic Academy or the post-Aristotelian Peripatos. In due course the Romans completed another conquest; but they too, at first more powerful than civilized, were eager to preserve what they felt to be the superior culture of Greece. Certainly, in the period while Rome was still under republican government, Greece shared to the full in the too frequent maladministration of the empire. But even at that time her thinkers and men of letters enjoyed in many ways an extraordinarily favored position. They had, as the Romans had not, a large and splendid literature; they had living philosophical schools and traditions; in every department of science and art they were exclusive possessors of the knowledge and expertise of the age. The Romans had sense enough to wish to preserve and make use of this imposing culture. They accepted, for all purposes of higher education, the use of the Greek language, and frequently, almost pathetically, adopted without question that grand division of the human race into "Greeks and barbarians" which, centuries earlier, had seemed proper to the Greeks at the height of their power. There has probably never occurred before or since, if we except the case of Christianity, so striking an instance of the cultural conquest of military conquerors. Anxious Roman patriots did, from time to time, attempt by decree to keep encroaching Hellenism at any rate out of Rome itself, but such efforts had no chance of long-run success. That Marcus Aurelius, the Emperor of Rome, should have spent much of his time expounding, in Greek, a Greek system of philosophy, would no doubt have horrified some of the early Roman statesmen; but the continuing pre-eminence of Greek culture made it in fact an entirely natural thing for him to do.
The history of philosophical schools in Roman times is a somewhat curious one. The rival traditions of Zeno and Epicurus stand out together for centuries as dominant over all others; but Stoicism, which certainly came to be the characteristic philosophy of the Roman empire, appears to have lagged far behind Epicureanism in the republican period. Cicero, writing in the last days of the republic, gives the impression that this latter system alone was widely popular and generally known, and indeed that it had at that time no effective competitor. The Stoics, it appears, were less skillful at popularization; but it may be true too that, at that particular time, the conditions that prevailed were just those in which Epicureanism might flourish. The last century of the Roman republic was a period, on the whole, of incessant violence and confusion. The domestic politics of Rome were peculiarly embittered, and her ill-governed empire also was in constant peril. Private fortunes, though sometimes very large, were hardly ever secure, and life itself was precarious even in the streets of Rome. In such conditions the essential moderation of Epicurus, his attempt to make the best of an unambitious, purely private existence, may well have exerted upon many a powerful appeal; it was indeed in very similar circumstances that the doctrine had originally come into being. By contrast the more positive, more active principles of the Stoics may have seemed unattractive to those whose faith in well-meant action had been shaken by too frequent disappointments. This is not to deny, of course, that many successful men of action were also, at that time, Epicureans.
If this were so, we could perhaps also account for the apparently swift change in the position at a later date. After the defeat of Antony at Actium in 31 B.C. the government of the first emperor, Augustus, brought to the world a condition of comparative order and stability such as had been unknown for many decades before. Almost at once the tone of Roman life became stronger, but also more constrained. There was indeed a new enthusiasm for public affairs, a general readiness to labor for the new and beneficent régime; but with this there went a constant pressure of official propaganda, moralistic, traditionally religious, rather stiffly self-righteous. In this atmosphere the taste of the Romans for intellectual inquiry, never marked at any time, fell practically to zero, while their devotion to duty, particularly the duties of public life, received every encouragement. Thus Stoicism, in which purely theoretical and scientific doctrine had never been so important as in the system of Epicurus, and in which conversely the stern preaching of virtue had always bulked large, became inevitably the favored philosophy of the day. At the same time the main motive towards Epicureanism — distrust of the perils and treacheries of the great world — was substantially diminished. It would be hard to deny that the resulting tendency towards a somewhat incurious, unimaginative moralizing represents a general decline in philosophy, though Stoic philosophers of a kind were still popular enough. So popular were they, indeed, that for many years controversy almost died out; the doctrines of philosophy were not felt to be matters of dispute, and the emphasis shifted instead onto the personality of the philosopher. It is worth observing too that this prevalent tendency was hostile, on the whole, to literature and to culture in general; the true Stoic regarded all that was not simple virtue as frivolity. We may remember that Marcus Aurelius, when he decided to devote himself seriously to philosophy, felt that this involved the deliberate rejection of those literary arts and interests in which he had been educated.
When Marcus Aurelius, the philosophical emperor, died, the dominance of Stoicism also began rapidly to decline. This decline may well have been connected with a general change for the worse in the conditions of life. The empire henceforward was in almost continuous peril from the pressure of barbarian hordes upon its frontiers. Total failure to solve the problem of orderly succession makes the history of later emperors one of violence, assassination, and civil conflict. It is from this period that Gibbon dates the "decline and fall" of Roman power; and indeed, in considering it, one cannot help feeling that, in spite of the temporary successes of exceptional administrators or military commanders, the downfall of Rome had by this time became inevitable. Furthermore, this seems to have been keenly felt at the time. Roman civilization not only was, but also knew itself to be, in decline; and the literature of the third century A.D. is full, in the pages of both pagan and Christian writers, of prophecies of doom. A striking feature of this unhappy period was a very strange but most vigorous revival of religious feeling. The old Roman pantheon, already almost identified with the Greek, was now subjected — not for the first time — to the encroachment of a number of deities and sets of deities from the East; and, in Rome particularly, a vast number of cults were practiced side by side in mutual toleration, often with the idea that all were perhaps mere variants on some single, vaguely conceived true worship. (Christianity alone not only rejected the divinity of other gods, but actually regarded the gods of other religions as evil demons. It was partly owing to this fervent exclusiveness that the Christians were apt to be singled out for persecution.) Inevitably, this wide-spread religiosity involved much that we should now consider to be gross superstition. Uncritical belief in so large a number of unseen powers ensured profits for those who purported to communicate with them, and astrology indeed held the place of "the queen of the sciences."
All this being so, it is perhaps not surprising that the next — and last — development in Greek philosophy should have been markedly otherworldly and mystical in character, as complete a break as could be with the morally directed materialism of the Stoics, and the scientifically based moral sobriety of Epicurus. This development took the form, ostensibly, of a return to Plato.
It was regarded as a return to Plato, not to the doctrines of the Academy. It was mentioned earlier that, after Plato's death, the Academy was for a time a center of Scepticism. Later still, in the first century B.C., it became eclectic, its leader Antiochus explicitly contending that between Academic, Stoic, and Peripatetic doctrines there was no real disagreement. This sort of view was all too tempting at a time when genuine intellectual interest was at a low level. It suits very well, for example, with the rather lazy, literary refinement of Cicero, who liked to think of himself as a Neo-Academic. It is probable that the weakness of the Academy at this period was partly due to the fact that Plato himself, being a real philosopher, had never laid down any Platonic dogma. His dialogues certainly would afford small comfort to those more eager for a doctrine than for intellectual stimulation. Apuleius of Madaura, near the end of the first century A.D., wrote a Latin work De Platone et Ejus Dogmate, but he was more a rhetorician than a philosopher. A later attempt was made, in the second century, by Atticus to rescue the school from its excessive eclecticism; but Plotinus, the great figure of so-called Neo-Platonism, never regarded himself as an adherent of the Academy. His immediate teacher was an Alexandrian, Ammonius Saccas, apparently a self-taught philosopher; and in his own work he owed more, as will become clear, to the Neo-Pythagoreans, whose singular numerological metaphysics was a development of that aspect of Pythagoreanism which had chiefly influenced Plato himself. They appear to have regarded Pythagoras as a divine being — a status which he shared, in their view, with certain numbers also, particularly one, three, and ten.