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
Thracian warfare (plus the onset of winter) meant that this army only held together for about six weeks and any Thracian conquests were ephemeral. The Sapaeans ruled Thrace after the Odrysians until its incorporation to the Roman Empire as a province. Thrace became a Client state of Rome at 11 BC and was annexed at 46 AD. Thrace had the potential to muster a huge number of troops though this rarely occurred. By tradition, Thracians honored warriors and, according to Herodotus, despised all other occupations. The Thracians fought as peltasts using javelins and crescent or round wicker shields called "peltes". Missile weapons