Elite Guards and Household Troops Across Two Thousand Years

The Immortals were kept at exactly 10,000 men because any loss was replaced at once, which is how Greek writers came to name them. They formed the royal guard and core strike force under Cyrus the Great, Darius I and Xerxes I, and their fate after Alexander ended the empire in 330 BC is not recorded.

Thebes built its elite unit from 150 pairs of male lovers, on the theory that men would fight hardest in front of their partners. The Band spearheaded the victories at Leuctra in 371 BC and Mantinea in 362 BC, and was destroyed to the last man at Chaeronea in 338 BC.

Macedon, whose forces ended the Sacred Band, developed this heavy cavalry under Philip II and raised it to its height under Alexander. Riding without stirrups and carrying the long xyston lance, the Companions charged in a wedge, usually led by Alexander himself, to decide the battles at the Granicus, Issus and Gaugamela.

Augustus formed the Praetorian Guard around 27 BC as the emperor's bodyguard, based at the Castra Praetoria in Rome. Its closeness to the throne made it a political force: it auctioned the throne to Didius Julianus in 193 CE, and Constantine I disbanded it in 312 CE after it backed Maxentius.

Basil II formed this guard in 988 from 6,000 Rus warriors sent by Vladimir I of Kiev. Foreigners with no stake in court politics made reliable bodyguards, and later recruits included Harald Hardrada and, after 1066, Anglo-Saxon exiles. The Guard is last clearly attested defending Constantinople in 1204.

The Hospitallers began as a charity caring for sick pilgrims in Jerusalem and became a military order after the First Crusade, recognized by Pope Paschal II in 1113. They garrisoned castles such as Krak des Chevaliers, held Rhodes from 1310 to 1522, and defended Malta in the Great Siege of 1565.

Founded around 1119 by Hugues de Payens to protect pilgrims, the Templars joined monastic vows to heavy cavalry warfare and built an early banking network. Philip IV of France, deeply in debt to the order, brought heresy charges from 1307, and Pope Clement V dissolved it in 1312.

Founded around 1190 during the Third Crusade, this German order turned its attention to the Baltic and conquered Prussia, ruling it as a state under its Grand Master. It lost to Novgorod at the Battle on the Ice in 1242 and to Polish and Lithuanian forces at Grunwald in 1410, and its Prussian state was secularized in 1525.

The Mamluks were slave soldiers, bought young and trained in mounted archery and swordsmanship, who took the Egyptian throne outright in 1250. Their cavalry gave the Mongols their first major defeat at Ain Jalut in 1260, and the system ended when Muhammad Ali Pasha destroyed the remaining beys in 1811.

Raised through the devshirme levy of Christian boys from the Balkans, converted and trained to serve the sultan alone, the Janissaries were early adopters of firearms and anchored Ottoman victories including Constantinople in 1453. Their growing political power made them a threat, and Mahmud II abolished the corps by force in 1826.