Wandering though ruins, along deserted thoroughfares and past toppled columns, can be a melancholy, if not disquieting, experience. For some it is the sense of vast futility of vanished and vanquished kingdoms, of which one might read in Shelley's Ozymandias. But ruins open other prospects, not least that sense of majesty and awe such as the Company felt as they swept along the River Anduin past the Argonath, the giant sentinels of Númenor. For some today such emotions are either a dangerous or a worthless currency, a price to be paid for our disenchantment. Yet for innumerable generations men and women have stood before temples and shrines, now derelict if not entirely vanished, to scry the Moon, perhaps as a heart-catching sliver at dusk or an immense harvest orb pulling itself above the horizon. The potency of the Moon needs no emphasis. Yet it has only recently come to be realized that it, too, is a gigantic and lifeless ruin, a shattered world, but a satellite whose existence, we now realized, has had a profound effect on the Earth and its four-billion-year-old cargo of life. Indeed, the peculiarities of the formation of the Moon help to epitomize the principal theme of this book, the odd fortuitousness of the world in which we find ourselves, where again and again matters seem to be remarkably well arranged.