Both “religion” and “secularism” are constructs distinctive of the West. They both arise from the peculiar history of Christianity. Hence the double face of modern “religion.” It may cover any inherited cultic practice, safeguard ethnic values, and be respected under multiculturalism. But at the same time it may refer to the intellectual and moral commitments which mark us off socially from others, annoying the secularists. Julian, the first modern-type secularist, reacted against the Constantinian establishment of the “new religion” by ordering the priests of the old Hellenic cults to adopt the Christian style of social indoctrination to outclass those vulgar innovators. But the Fall of Rome produced the intellectual masterpiece of Augustine which redefined the saeculum and set the framework of modern secularity. Augustine had perceived reality in three dimensions: cosmic, social, and personal. At each level the rationalising logic of Aristotelian science had fixed the pattern of things, by analogy. The whole must be coherent if it is to be true. But the empiricism of Jerusalem had delivered a universe open to change and likely to end. In society power was no longer the proof of virtue. The heart itself was deceptive. Twenty-first century secularism insists upon such experimental truth, social choice and passionate commitment. This holy trinity is our legacy from the “new” religion.