7 points
These were the 10,000 elite Persian soldiers that served as the King's
personal bodyguards. They also fought the Spartans during the battle of
Thermopylae. *

The elite Persian soldiers were called the Immortals.

Explanation:

These soldiers were called the Immortals because according to ancient Greek historian Herodotus they were immediately replaced if one became wounded or they were killed making them seem like a permanent standing army of immortal force.  They also served as a kind of National Guard for the Achaemenid Empire. Immortals participated in the Battle of Thermopylae 480 BC but the Persian forces were eventually defeated despite outnumbering the Greek forces. The Immortals were also a part of the Persian occupation forces in Greece in 479 BC according to existing accounts.

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