Battle of Gaugamela main Persian infantry was poorly trained and equipped in comparison to Alexander's pezhetairoi and hoplites. The only respectable infantry Darius had were his 2,000 Greek hoplites and his personal bodyguard, the 10,000 Immortals. The Greek mercenaries fought in a phalanx, armed not with a heavy shield but with spears no longer than three metres, while the spears of the Immortals were two metres long. Among the other Persian troops, the most heavily armed were the Armenians, who were armed the Greek way and probably fought as a phalanx. The rest of Darius' contingents were much more lightly armed; the main
Peltast example, in the Hellenica [3.2.16] Xenophon writes 'When Dercylidas learned this (that a Persian army was nearby), he ordered his officers to form their men in line, eight ranks deep (the hoplite phalanx), as quickly as possible, and to station the peltasts on either wing along with the cavalry. They could also operate in support of other light troops, such as archers and slingers. When faced by hoplites, peltasts operated by throwing javelins at short range. If the hoplites charged, the peltasts would retreat. As they carried considerably lighter equipment than the hoplites, they were usually able to evade successfully,