The Persian Immortals

Immortals: Greek name for an elite regiment in the ancient Achaemenid empire. In his description of the battle of Thermopylae (480 BCE), the Greek researcher Herodotus mentions a Persian elite corps which he calls the Ten Thousand or the Athanatoi, the 'Immortals'. He describes them as a body of picked Persians under the leadership of Hydarnes, the son of Hydarnes. This corps was known as the Immortals, because it was invariably kept up to strength; if a man was killed or fell sick, the vacancy he left was at once filled, so that the total strength of the corps was never less -and never more- than ten thousand.