Alexander has lent credence to the theory that history is shaped by great men. Because no one was capable of taking his place, the great empire that he established fell apart after his death.

His forays into the Far East made little lasting difference to the people there, except that, according to Mercer, he has lived on as a folk-villain in the collective memory of the Afghans. But Persia has never again been the same as it was under Alexander's arch-rival Darius, a change that has had an impact on subsequent history. In modern times, the Shah of Iran considered himself descended from Darius and once held a great celebration for his own birthday in the ruins of Persepolis, Darius's capital city. But the descendants of Darius have never succeeded in re-establishing their country as the world power that it was before Alexander sacked Persepolis.

In 356 B.C...