Forgotten Empire, the new exhibition in London devoted to the great realm that Alexander the Great destroyed, is an openly political occasion, designed to stress links in the present as well as to revive interest in a part of the past that has more or less sunk into oblivion. It stresses the fact that, despite the tensions that now exist between the Islamic Republic of Iran and Western Europe, a degree of cultural cooperation is still possible. In doing so, it offers a gentle rebuke to the attitudes that prevail in the United States, Britain’s closest military and political ally. In these circumstances, it cannot fail to be a fascinating occasion, resonant with hidden meanings.