Which elite Persian unit did Hydarnes lead around the mountain path?

Hydarnes led the Immortals along the mountain path around Thermopylae. This elite Persian unit attacked the Greek position during the Battle of Thermopylae in 480 BCE.

The Immortals were the Achaemenid king’s crack infantry force, traditionally described by Herodotus as numbering 10,000. Their name referred to the practice of immediately replacing fallen or incapacitated soldiers, keeping the unit at a constant strength.

A local Greek named Ephialtes revealed the Anopaea path to the Persians. Hydarnes then guided the Immortals over the route, allowing Xerxes’ forces to outflank Leonidas and the remaining Greek defenders. The path was not a secret mountain road invented for the battle; it was a known route used by local people.

The Immortals are often confused with later famous units such as the Spartan Three Hundred or the Sacred Band of Thebes. They were Persian royal troops, not Greeks, and their decisive role came from the flanking march rather than from breaking through the main Greek front.