Tracking an empire -- Forerunners of the Achaemenids : the first half of the first millennium BCE -- Persia rising : a new empire -- From Cyrus to Darius I : empire in transition -- Darius, the great king -- Mechanics of empire -- Xerxes, the expander of the realm -- Anatomy of empire -- Empire at large : from the death of Xerxes to Darius II -- Maintaining an empire : Artaxerxes II and Artaxerxes III -- Twilight of the Achaemenids.