The Companion cavalry, or Hetairoi (Ἑταῖροι), were the elite arm of the Macedonian army, and have been regarded as the finest quality cavalry in the ancient world.
Along with Thessalian cavalry contingents, the Companions — raised from landed nobility — made up the bulk of the Macedonian heavy cavalry.
Central Macedonia was good horse-rearing country and cavalry was prominent in Macedonian armies from early times.
However, it was the reforms in organisation, drill and tactics introduced by Philip II that transformed the Companion cavalry into a battle-winning force, especially the introduction of, or increased emphasis on, the use of a lance and shock tactics.
Coinage indicates that from an early period the primary weapons used by Macedonian cavalry were a pair of javelins.
This remained true through to the reign of Archelaus I (413–399).
Subsequently, despite the adoption of the lance, it is highly probable that the Companion cavalry continued to employ javelins when on scouting or skirmishing missions.

The hetairoi were divided into squadrons called ilai (singular: ilē), each 200 men strong, except for the Royal Squadron, which numbered 300.
The Royal Squadron was also known as the Agema - "that which leads".
Each squadron was commanded by an ilarchēs (ilarch) and appears to have been raised from a particular area of Macedon.
Arrian, for instance, described squadrons from Bottiaea, Amphipolis, Apollonia and Anthemus.
It is probable that Alexander took eight squadrons with him on his invasion of Asia totalling 1,800 men, leaving seven ilai behind in Macedon (the 1,500 cavalrymen mentioned by Diodorus).
Between 330 BC and 328 BC, the Companions were reformed into regiments (hipparchies) of 2-3 squadrons.
In conjunction with this, each squadron was divided into two lochoi.
This was probably undertaken to allow for the increase in size of each squadron, as reinforcements and amalgamations meant that the Companion cavalry grew in size.
At this time, Alexander abandoned the regional organisation of the ilai, choosing their officers regardless of their origins.

The individual Companion cavalry squadrons were usually deployed in a wedge formation, which facilitated both manoeuvrability and the shock of the charge.
The advantage of the wedge was that it offered a narrow point for piercing enemy formations and concentrated the leaders at the front.
It was easier to turn than a square formation because everyone followed the leader at the apex, "like a flight of cranes".
Philip II introduced the formation, probably in emulation of Thracian and Scythian cavalry, though the example of the rhomboid formation adopted by Macedon's southern neighbours, the Thessalians, must also have had some effect.

The primary weapon of the Macedonian cavalry was the xyston, a double ended cornel-wood lance, with a sword as a secondary weapon.
From descriptions of combat, it would appear that once in melee the Companion cavalryman used his lance to thrust at the chests and faces of the enemy.
It is possible that the lance was aimed at the upper body of an opposing cavalryman in the expectation that a blow which did not wound or kill might have sufficient leverage to unseat.
If the lance broke, the Companion could reverse it and use the other end, or draw his sword.
Cleitus, an officer of the Companions, saved Alexander the Great's life at the Granicus by cutting off an enemy horseman's arm with his sword.
Companion cavalrymen would normally have worn armour and a helmet in battle.

Although the Companion cavalry is largely regarded as the first real shock cavalry of Antiquity, it seems that Alexander was very wary of using it against well-formed infantry, as attested by Arrian in his account of the battle against the Malli, an Indian tribe he faced after Hydaspes.
There, Alexander did not 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.
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The Companion cavalry, or Hetairoi (Ἑταῖροι), were the elite arm of the Macedonian army, and have been regarded as the finest quality cavalry in the ancient world. Along with Thessalian cavalry contingents, the Companions — raised from landed nobility — made up the bulk of the Macedonian heavy cavalry. Central Macedonia was good horse-rearing country and cavalry was prominent in Macedonian armies from early times. However, it was the reforms in organisation, drill and tactics introduced by Philip II that transformed the Companion cavalry into a battle-winning force, especially the introduction of, or increased emphasis on, the use of a lance and shock tactics. Coinage indicates that from an early period the primary weapons used by Macedonian cavalry were a pair of javelins. This remained true through to the reign of Archelaus I (413–399). Subsequently, despite the adoption of the lance, it is highly probable that the Companion cavalry continued to employ javelins when on scouting or skirmishing missions.
The hetairoi were divided into squadrons called ilai (singular: ilē), each 200 men strong, except for the Royal Squadron, which numbered 300. The Royal Squadron was also known as the Agema - "that which leads". Each squadron was commanded by an ilarchēs (ilarch) and appears to have been raised from a particular area of Macedon. Arrian, for instance, described squadrons from Bottiaea, Amphipolis, Apollonia and Anthemus. It is probable that Alexander took eight squadrons with him on his invasion of Asia totalling 1,800 men, leaving seven ilai behind in Macedon (the 1,500 cavalrymen mentioned by Diodorus). Between 330 BC and 328 BC, the Companions were reformed into regiments (hipparchies) of 2-3 squadrons. In conjunction with this, each squadron was divided into two lochoi. This was probably undertaken to allow for the increase in size of each squadron, as reinforcements and amalgamations meant that the Companion cavalry grew in size. At this time, Alexander abandoned the regional organisation of the ilai, choosing their officers regardless of their origins.
The individual Companion cavalry squadrons were usually deployed in a wedge formation, which facilitated both manoeuvrability and the shock of the charge. The advantage of the wedge was that it offered a narrow point for piercing enemy formations and concentrated the leaders at the front. It was easier to turn than a square formation because everyone followed the leader at the apex, "like a flight of cranes". Philip II introduced the formation, probably in emulation of Thracian and Scythian cavalry, though the example of the rhomboid formation adopted by Macedon's southern neighbours, the Thessalians, must also have had some effect.
The primary weapon of the Macedonian cavalry was the xyston, a double ended cornel-wood lance, with a sword as a secondary weapon. From descriptions of combat, it would appear that once in melee the Companion cavalryman used his lance to thrust at the chests and faces of the enemy. It is possible that the lance was aimed at the upper body of an opposing cavalryman in the expectation that a blow which did not wound or kill might have sufficient leverage to unseat. If the lance broke, the Companion could reverse it and use the other end, or draw his sword. Cleitus, an officer of the Companions, saved Alexander the Great's life at the Granicus by cutting off an enemy horseman's arm with his sword. Companion cavalrymen would normally have worn armour and a helmet in battle.
Although the Companion cavalry is largely regarded as the first real shock cavalry of Antiquity, it seems that Alexander was very wary of using it against well-formed infantry, as attested by Arrian in his account of the battle against the Malli, an Indian tribe he faced after Hydaspes. There, Alexander did not 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. A
Ancient Macedonian army