Armies - The Persian Army
The armies of the Persian foe were made up of levies of numerous peoples, all dressed and armed according to their national custom. Thus, the Persian army can be seen as a celebration of the heterogenous harmony that - with only a few exceptions - had existed throughout the huge empire: indeed, a sort of 'United Nations peace keeping force' of Antiquity. Just as modern soldiers are willing to sacrifice their lives for abstract ideals - liberty, democracy, freedom - the original Persian soldier was also willing to die for a higher goal: his King. (Maybe one might compare this with the determination of the Japanese in World War II to fight and die for their Emperor.)
The nucleus of Darius' army were the Immortals or Apple-Bearers, the Persian élite counterpart of the Macedonian hypaspists. Traditionally they numbered 10,000 and Darius III fielded something in between 2,000 and 10,000 as his Royal Guards. Immortals carried a spear (with golden or silver apples at the butt), lavish tunics, a bow and a wicker shield. For their fighting skills the Persians hired Greek mercenary hoplites. Darius employed 10,000 of them at Issus, and these heavy infantry enemies were one of the main concerns of Alexander.
The remaining bulk of the forces were cavalry and light infantry from all corners of the empire. Prior to Issus and Gaugamela Curtius Rufus lists heavy Bactrian cavalry, Scythian mounted archers, excellent Hyrcanian cavalry, skilled Mardian archers, Barcanian horsemen armed with double-headed axes, Cossaean tribal levies, Cadusians, Cappadocians, Indians - and the list goes on and on, including "tribes unfamiliar even to their own allies". Persian cavalry was of remarkable standard; though probably not as well disciplined to attack in formation like the Companions, they outclassed Alexander's mercenary and allied horse.
At Gaugamela Darius used about 200 scythed chariots, equipped with sharp rotating spikes to demolish anything that came in their way. They were no challenge however for Alexander's mobile peltasts and Agrians. Heading the army were fifteen war elephants which could not make a lasting impression either.
Written by nick