Achaemenids (ăk´əmĕn´Ĭdz), dynasty of ancient Persia. They were descended presumably from one Achaemenes, a minor ruler in a mountainous district of SW Iran. His successors, when Elam declined, spread their power westward. Cyrus the Great established the Persian rule by his conquest of Astyages of Media. The Achaemenids (c.550–330 BC) were important for their development of government administration, the appearance of literature written in cuneiform, and the spread of Zoroastrianism; during this period there was also a great flourishing of Persian art and architecture. The Achaemenid rulers after Cyrus were Cambyses II, the impostor Smerdis, Darius I, Xerxes I, Artaxerxes I, Xerxes II, Sogdianus, Darius II, Artaxerxes II (opposed by Cyrus the Younger), Artaxerxes III, Arses, and Darius III. The dynasty ended when Darius III died in his flight from Alexander the Great.