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
Classification of Thracian Dacian which he regards as belonging to a separate language family as Thraco-Armenian. Older textbooks grouped Phrygian and Armenian with Thracian, but the belief is no longer popular and is mostly discarded. Today, Phrygian is not widely seen as linked to Thracian. Georgiev claimed that Thracian is different from Phrygian "as much as Greek from Albanian", comparing 150 Phrygian inscriptions. Duridanov found in 1976 Phrygian completely lacking parallels in Thracian and concluded that the Thraco-Phrygian theory is debunked. Duridanov argued that the Thraco-Illyrian theory is a mistake of the past: "In the past it was regarded that Thracian together with