You can’t observe historical events; you can’t question historical actors; you can’t even know most of what has not been written about. What has been written about therefore takes on an importance that may be spurious. A few lines in a memoir, a snatch of recorded conversation, a letter fortuitously preserved, an event noted in a diary: all become luminous with significance—even though they are merely the bits that have floated to the surface. The historian clings to them, while, somewhere below, the huge submerged wreck of the past sinks silently out of sight.