Relief of Immortals, the Apadana, Persepolis, Iran. The Immortals were an elite royal guard within the Achaemenid Persian army. Only ethnic Persians or Medeans could be members of the unit which, according to the Greek historian Herodotus, always numbered precisely 10,000 men. The Immortals fought against the Greeks at the battles of Marathon and Thermopylae, and were defeated by Alexander the Great at the Battle of Issus in 333 BC.
