Companion cavalry The Companions ( , " hetairoi " ) were the elite cavalry of the Macedonian army from the time of king Philip II of Macedon and reached the most prestige under Alexander the Great , and have been regarded as the best cavalry in the ancient world and the first shock cavalry . Chosen Companions / Hetairoi formed the elite guard of the king ( Somatophylakes ) . Etymology . The name of the military unit derives from the " Hetairoi " , those near the king . The Hetairoi ( Companions ) could be members of the Macedonian aristocracy or commoners of any Greek origin who enjoyed the trust and friendship of the Macedonian regent . The Hetairideia , a festival pertaining to the sacred relationship which bound the king and his companions together was celebrated and even Euripides , the famed Athenian play writer , was honoured as an " hetairos " of the king Archelaus . The Royal friends ( Philoi ) or the king ' s Companions ( basilikoi hetairoi ) were named for life by the king among the Macedonian aristocracy . Unit . Equipment . Companion cavalry would ride the best horses , and receive the best weaponry available . In Alexander ' s day , each carried a xyston , and wore a bronze muscle cuirass or linothorax , shoulder guards and Boeotian helmet s , but bore no shield . A kopis ( curved slashing sword ) or xiphos ( cut and thrust sword ) was also carried for close combat , should the xyston break . Organization . The Companion cavalry was composed of the Hetairoi of the king , mainly upper class citizens who were able to acquire and maintain armour and horses . In the age of Philip II and Alexander they were organized into 8 territorial squadrons , termed " ilai " . Each " ile " numbered between 200 and 300 horsemen and was commanded by two men , because as Arrian claims , Alexander " did not want anyone , not even his intimate friend , to be the centre of attention " . After receiving reinforcements in Susa , Alexander established two companies in each squadron . They were referred to by the name of the territory they were mustered in or by the name of its captain . The Royal Ile was commanded by Alexander himself and contained twice the number of soldiers of the other units contained , c . 400 . These cavalry squadrons would sometimes be combined together in groups of two , three or four to form a " hipparchy " , which was commanded by a " hipparch " , though the whole Companion force was generally commanded by Alexander . In Alexander ' s Balkan campaigns , we find mention of Companions from upper Macedonia , the central Macedonian plain and Amphipolis . During the advance on Granicus , a squadron commanded by Socrates of Macedon ( not to be confused with the philosopher ) hailed from Apollonia on Lake Bolbe . During the Battle of Issus Arrian names the ile of Anthemus ( modern Galatista ) , and another from the unidentified land of Leuge , likely Pieria are also mentioned . Theopompus describes the Companions , probably of around the mid 4th century BC , as being made of " no more than 800 at this time " and mustered " some from Macedonia , some from Thessaly and still others from the rest of Greece " . By 338 BC , Alexander is reported to have around 2600 in his Companion Cavalry . As Alexander ' s force campaigned towards India , barbarians played an increasing role in the Companion Cavalry and the Macedonian mutiny at Opis may have been partially caused by this . At one point there were four " hipparchies " made up of entirely oriental forces and one that was a mix of Macedonians and orientals . Tactics and use . The Companions probably constituted the first real shock cavalry in history , able to conduct charges against massed infantry , even if such use is scarcely described in the ancient sources . Contemporary cavalry , even when heavily armored , would most usually be equipped with javelins and would avoid melee . In battle , it would form part of a hammer and anvil tactic : the Companion cavalry would be used as a hammer , in conjunction with the Macedonian phalanx - based infantry , which acted as their anvil . The phalanx would pin the enemy in place , while the Companion cavalry would attack the enemy on the flank or from behind . In battle , Alexander the Great personally led the charge at the head of the royal squadron of the Companion cavalry , usually in a wedge formation . In a pitched battle , the Companions usually fought on the right wing of the Macedonian army , next to the shield bearing guards , the Hypaspists , who would guard the right flank of the phalanx . Other cavalry troops would protect the flanks of the Macedonian line during battle . Under Alexander ' s command , the Companions ' role was decisive in most of his battles in Asia . Legacy . Hellenistic kingdoms . The Companion cavalry of the Diadochoi ( Alexandrian successor - states ) , were even more heavily equipped . Seleucid Companions were noted to have worn lighter , but not otherwise dissimilar , equipment to the cataphract s at the Battle of Magnesia in 190 BC , which may have included partial horse armour and leg and arm protection . Ptolemaic Companions were also equipped with a large round " aspis " cavalry shield unlike the Companions of Phillip and Alexander . ‘ Companions ’ was a title not used by the Seleucids in its original sense . It was replaced with different and various grades of ‘ Kings Friends ' . However , the title Companions was kept as a regimental one . There was only one regiment or unit that held the title of Companions in the entire Hellenistic world though ; the Antigonids and Ptolemies had different names for their elite cavalry regiments . Eastern Roman Empire . The " Hetaireia " or " Hetaeria " was a corps of bodyguards during the Byzantine Empire . Its name means " the Company " , echoing the ancient Macedonian Companion cavalry . The imperial " Hetaireia " was composed chiefly of foreigners . They acted as part of the Byzantine imperial guard alongside the " tagmata " in the 9th – 12th centuries .