Gabriele Esposito presents a detailed overview of the history, organization, equipment and tactics of the military forces deployed by Achaemenid Persia during the period 550-330 BC. The Achaemenid Empire founded by Cyrus the Great was one of the major military powers of Antiquity, conquering vast territories that straddled three continents. Its large and varied population supplied a dazzling array of troop types, producing a versatile war machine that campaigned from India to Egypt. These were the armies that drank rivers dry as they invaded Greece and, at the Empire’s zenith, defeated the Spartans at Thermopylae and torched Athens. They continued to evolve but proved unable to cope with Alexander the Great’s Macedonians. The author outlines the major campaigns fought by the Persians from Cyrus the Great to the conquest by Alexander. He details the organization, equipment and tactics of the many different contingents that made up the Persian military forces, including (but not limited to) the famous royal guard of the Immortals, and such varied troops as Persian archers, scythed chariots, Ionian Greek hoplites, Arab camel riders, Scythian horse archers, Sogdians and Bactrian armoured cavalry, Thracian peltasts, Egyptians and Indian war elephants. The text is complemented by a colourful mix of photos of reenactors and specially-commissioned artworks.