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
Light infantry heavier at the same time as hoplite equipment grew lighter. It was the fact that peltasts fought in open order as skirmishers that made them light infantry and that hoplites fought in the battle line in a phalanx formation that made them heavy infantry. Early regular armies of the modern era frequently relied on irregulars to perform the duties of light infantry skirmishers. In the 17th century, dragoons were the light infantry skirmishers of their day – lightly armed mounted infantrymen who rode into battle but dismounted to fight, giving them a mobility lacking to regular foot soldiers. In the