Hetairoi
The hetairoi (ἑταῖροι, hetairoi, 'companions') made up the elite cavalry of Alexander the Great's army. In addition to being an offensive weapon, they served as the Macedonian's personal guard. Used in conjunction with the Macedonian phalanx, it "pinned" the enemy in place, staying in defensive formation, and the companion cavalry charged on their flank or behind. The cavalry therefore received the name of "hammer" in strategies, because it literally crushed the enemy units held back by the "anvil" or the "phalanx". Normally, Alexander led the charge, forming his horsemen into a wedge. His existence ranges from the reign of Philip II to that of his son and his successor, according to Diodoro Siculo and Flavio Arriano. The elite hetairoi formed the guard of the Macedonian monarchs (somatophylakes).
Etymology
The name of this military unit hetairoi means those who are close to the king. They were 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 about the sacred relationship that always united the king and his companions, was celebrated, and even Euripides, the famous writer of Greek tragedies, was honored as hetairos by King Archelaus I. Royal friends (philoi) or companions of the king (basilikoi hetairoi) were appointed for life by the king from among the Macedonian aristocracy.
Organization
The hetairoi were organized in squads of two to three hundred soldiers. In the Persian campaign there were eight squadrons, commanded by Philotas, one being the royal squadron (formed by Alexander's close friends, sons of Macedonian nobles).
At the same time, these troops protected the flanks of the front line during battle. The hetairoi rode the best horses, bareback or on a blanket, and were issued with the best weaponry available. Each one carried a long throwing spear (xyston), a sword kopis (similar to the Iberian falcata) for hand-to-hand combat, linen or bronze cuirass, protective bracers and helmet. The horses were also partially protected.
As heavy cavalry, the hetairoi proved Alexander the Great's decisive weapon in battle.