Here, frozen in time, is a moment of forgotten greatness in human history. The remarkable photograph on the facing page was taken almost exactly 100 years ago, at 2pm on May 20, 1922, on the roof of the world. But not the very top. Not quite. Leaning on their ice axes on a 45-degree rock face, Edward Norton and George Mallory gaze upwards towards their goal: the summit of Mount Everest, the world’s highest mountain. Because of overhanging rocks, they cannot actually see the top, but they reckon that vertically it is no more than 2,000ft away. They know, too, that it is tantalisingly out of their reach. It is…