Persian Immortals (pre-Sasanian tradition)

Timeline

1. c. -500–-330Susa · Iranian PlateauHerodotus records 10,000 standing infantry directly under the Persian king, wearing splendid dress and gold ornaments, immediately replaced from reserves after losses to keep the establishment fixed at 10,000.
2. c. 1–224Ctesiphon · MesopotamiaThe Parthian Empire continued the Persian elite guard tradition; the royal guard and noble cavalry together formed the core of court military power, serving as bodyguards of the center in wars against Rome.
3. c. 224–500Ctesiphon · MesopotamiaThe Sasanian Empire established a more systematic royal guard and elite infantry establishment; though perhaps no longer called 'Immortals', the elite tradition of a 10,000-strong standing force with immediate replacement continued in the guard units.