Companion cavalry
The Hypaspists ("Hypaspistai") were the elite arm of the Macedonian infantry. The word 'hypaspists' translates into English as 'shield-bearers'. During a pitched battle, such as Gaugamela, they acted as guard for the right flank of the phalanx and as a flexible link between the phalanx and the Companion cavalry. They were used for a variety of irregular missions by Alexander, often in conjunction with the Agrianians (elite skirmishers), the Companions and select units of phalangites. They were prominent in accounts of Alexander's siege assaults in close proximity to Alexander himself. The Hypaspists were of privileged Macedonian blood and their senior chiliarchy (χιλιαρχία) formed the "Agema" foot bodyguard of Alexander III.