An aetiological story professes to explain causes. The Pentateuch, especially Genesis, is rich in stories designed to give explanations about the origin of natural phenomena and of customs in religious worship. How did the rainbow come into existence, and what is its meaning? Gen. 9: 13 supplies the answer: it is a sign of the covenant between God and his creation that there shall never again be a universal flood. Such a story is called aetiological, from the Greek word aitia, meaning ‘a cause’, as in Acts 28: 20. An example of a cultic aetiology is the account of the Passover which answers the question in Exod. 12: 26. And if people asked why Bethel was held to be a sacred place, the story of Jacob (or Israel) having a dream there (Gen. 28: 10 ff.) supplied an answer. While many aetiologies are legends, some may be incorporated into narratives which have a basis in history, as in Josh. 4: 9, describing the existence of twelve stones in the Jordan.