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 pelte, two javelins and a sword. Body armor was restricted to nobles and army commanders. Greek armor was in use in Thrace before the classical age. Nobles would sometimes wear pectorals on their chests as a sign of rank. There was no Thracian navy but there were instances of Thracians turning to piracy. The Greek cities of the coast that paid tribute to the Thracian kings did sometimes provide the Thracian kings with ships. Even though Thracians attempted to build only one polis, they had forts in hills built as places of refuge. Thracian villages had basic fortifications as Xenophon