In its very first words this book announces itself as a ‘Revelation’ (apocalypsis), and within a hundred years of its composition this became the title by which it has been known ever since. The idea behind the word is as old as religion itself. There have always been certain men and women who have claimed that in the course of some supernatural experience divine mysteries were ‘revealed’ to them; and the religions of Greece and Rome, as of Egypt and the Middle East, produced numerous books of which the writers (whether under their own or assumed names) claimed to have fallen into a trance, to have seen inexpressible visions and to have been instructed by heavenly voices, apparitions or angels in the meaning of the mysteries they had seen or heard. To this extent there would have been nothing surprising in the appearance of such a book in a collection of the literature of the Christian religion. Nevertheless this book, though it was published and probably originally written in Greek, owed more to a particular Jewish tradition than it did to any precedents in the Greco-Roman world. To a Jewish thinker, the ultimate mystery to be revealed was not (as it might have been to a Greek philosopher or mystic) the reality lying behind the appearance of the physical world, or the destiny of the individual soul after death, or even (as was of great interest in an age much preoccupied with astrology) the pattern inexorably fixed on history by the movements of the stars.