When ancient peoples defended what they called their liberty, the word stood for a plain and urgent interest of theirs: that their cities should not be destroyed, their territory pillaged, and they themselves sold into slavery. For the Greeks in particular liberty meant even more than this. Perhaps the deepest assumption of classic philosophy is that nature and the gods on the one hand and man on the other, both have a fixed character; that there is consequently a necessary piety, a true philosophy, a standard happiness, a normal art. The Greeks believed, not without reason, that they had grasped these permanent principles better than other peoples. They had largely dispelled superstition, experimented in government, and turned life into a rational art. Therefore when they defended their liberty what they defended was not merely freedom to live. It was freedom to live well, to live as other nations did not, in the public experimental study of the world and of human nature. This liberty to discover and pursue a natural happiness, this liberty to grow wise and to live in friendship with the gods and with one another, was the liberty vindicated at Thermopylae by martyrdom and at Salamis by victory. As Greek cities stood for liberty in the world, so philosophers stood for liberty in the Greek cities. In both cases it was the same kind of liberty, not freedom to wander at hazard or to let things slip, but on the contrary freedom to legislate more precisely, at least for oneself, and to discover and codify the means to true happiness. Many of these pioneers in wisdom were audacious radicals and recoiled from no paradox. Some condemned what was most Greek: mythology, athletics, even multiplicity and physical motion. In the heart of those thriving, loquacious, festive little ant-hills, they preached impassibility and abstraction, the unanswerable scepticism of silence. Others practised a musical and priestly refinement of life, filled with metaphysical mysteries, and formed secret societies, not without a tendency to political domination. The cynics railed at the conventions, making themselves as comfortable as possible in the rôle of beggars and mocking parasites. The conservatives themselves were radical, so intelligent were they, and Plato wrote the charter of the most extreme militarism and communism, for the sake of preserving the free state. It was the swan-song of liberty, a prescription to a diseased old man to become young again and try a second life of superhuman virtue. The old man preferred simply to die.