In the second half of the 6th century BC, one of the greatest empires in world history was created by Persian kings from the Achaemenid dynasty. During the conquests of Cyrus II the Great (558? 530 BC) and his heirs, for only about forty years, the Persians conquered states and tribes in a huge space from Asia Minor to India. The rebellious local population was destroyed, mutilated or moved to other areas of the Persian Empire. The Persian army was the most advanced in the entire ecumene, and after the conquest of Media and Babylonia, it absorbed the military achievements of the Medes and Assyrians. The royal guard of the Achaemenids was called "immortals," since its number always remained constant (10 thousand soldiers) - the retired guard was immediately replaced by a recruit. The Persians knew how to storm fortified cities using siege engines, embankments and entrenchments. The navy assisted them in conducting ground offensive operations, delivering warriors and provisions. The Persians carefully planned their military campaigns, collecting information about the enemy with the help of intelligence services ("tsarevo eye" and "tsarevo ear "). The new book of the famous specialist in the military history of ancient peoples, Doctor of Historical Sciences A.K. Nefyodkin for the first time in Russian literature in all details covers the organization of the army of Iranians of the early era, Persians of Achaemenid (VI-IV centuries BC) and Sasanian (III-VII centuries) eras: types of troops and their tactics, siege and defense, intelligence, methods of conducting campaigns both on land at sea, customs related to the war, as well as a number of aspects of military ideology.