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
Ancient Macedonian army dare assault the dense infantry formation with his cavalry, but rather waited for his infantry to arrive, while he and his cavalry harassed their flanks. It is a common mistake to portray the Companion cavalry as a force able to burst through compact infantry lines. Alexander usually launched the Companions at the enemy after a gap had opened up between their units or disorder had already disrupted their ranks. However, the ancient historian Arrian implies that the Companion cavalry were successful in an assault, along with heavy infantry, on the Greek mercenary hoplites serving Persia in the closing stages of