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 Greek warfare turn therefore needed to defeat the Greek fleet; similarly, the Greeks needed to neutralise the Persian fleet to ensure their safety. To this end, the Greeks were able to lure the Persian fleet into the straits of Salamis; and, in a battleground where Persian numbers again counted for nothing, they won a decisive victory, justifying Themistocles' decision to build the Athenian fleet. Demoralised, Xerxes returned to Asia Minor with much of his army, leaving his general Mardonius to campaign in Greece the following year (479 BC). However, a united Greek army of c. 40,000 hoplites decisively defeated Mardonius at the