The study of history is a powerful antidote to contemporary arrogance. It is humbling to discover how many of our glib assumptions, which seem to us novel and plausible, have been tested before, not once but many times and in innumerable guises; and discovered to be, at great human cost, wholly false. It is sobering, too, to find huge and frightening errors constantly repeated; lessons painfully learnt forgotten in the space of a generation; and the accumulated wisdom of the past heedlessly ignored in every society, and at all times.