The legend tells about a horde of immortal warriors who do not die from spears and arrows, and they were kept constantly at a strength of exactly 10,000 men.
Herodotus claimed that the unit's name stemmed from the custom that every killed, seriously wounded, or sick member was immediately replaced with a new one, maintaining the numbers and cohesion of the unit.
The force consisted mainly of the Medes, the Persians and Elamites. But the first thousand warriors, who were the personal guards of the king, were formed exclusively from the Persian nobility.
Those who were assigned to become warriors started their army preparation since the childhood. It was mandatory for "immortal" to obtain a good ability of shooting a bow and riding a horse. Later they were also required to follow the strict adherence to the teachings of the great Zarathustra.
"Immortals" took part in the most important battles of the Persian Empire, in particular, in the war against the Neo-Babylonian kingdom, in the conquest of Egypt, in the campaigns of Darius I in India and Scythia, but they were especially known for their participation in the Greco-Persian wars.
Features and references in modern culture
The “Immortals” are most vividly portrayed in the 2006 film "300 Spartans". Director Zack Snyder portrayed them as demonic creatures in iron masks and black robes.