IRAN: The Eternal Land

Few names from ancient Persian military history have captured the imagination like the Immortals.

According to the Greek historian Herodotus, they were an elite corps of 10,000 Persian infantrymen during the reign of Xerxes. Whenever one soldier died, became ill, or otherwise left the ranks, another replaced him so that the unit’s nominal strength remained 10,000. This, Herodotus explained, was why they became known to the Greeks as the “Immortals.”

The story sounds almost mythical, but behind it was something very practical: military organization.

An Army Built on Organization

The Achaemenid military drew forces from many peoples across the empire. Greek sources describe a hierarchical organization involving commanders of groups of ten, one hundred, one thousand, and ten thousand.

Within this enormous military structure, the elite 10,000 held a special position.

Herodotus describes selected Persian soldiers accompanying Xerxes during his campaign against Greece in 480 BCE. Among them, 1,000 carried spears decorated with golden pomegranates, while the others had silver ornaments.

Their equipment was very different from the fantasy costumes sometimes shown in modern movies. Persian troops are described with soft headgear, sleeved tunics, trousers, wicker shields, bows, arrows, spears, and daggers.

Were the Guards at Persepolis the Immortals?

Visitors to Persepolis and museums often see images of beautifully dressed Achaemenid guards and hear them identified as the Immortals.

That identification is possible—but it is not proven.

Scholars have repeatedly associated guards depicted at Susa and Persepolis with the famous 10,000, but no surviving inscription identifies those figures specifically as the Immortals.

This distinction matters because much of what we know about the unit comes from Greek accounts rather than surviving Persian descriptions.

Even their original Iranian name remains uncertain.

The Immortals at Thermopylae

Their most famous appearance comes during the Battle of Thermopylae in 480 BCE.

Herodotus reports that the Immortals, commanded by Hydarnes, were sent against the Greek defenders. Fighting through the narrow pass proved difficult, but the Persians were eventually shown a mountain route around the Greek position.

Hydarnes led his forces along that path, allowing the Persian army to approach the defenders from behind.

Modern popular culture has transformed Thermopylae into legend, often portraying Persian soldiers in highly fictionalized ways.

The historical reality was more complex. The Achaemenid army was a large, organized, multinational force whose soldiers came from many regions of the empire.

What Made Them “Immortal”?

There was nothing supernatural about them.

Their immortality, at least according to Herodotus, came from replacement.

A soldier could fall, but the unit continued.

That idea reveals something important about Achaemenid Persia. Its power did not depend only on individual warriors or kings. It depended on systems designed to continue functioning.

The Royal Road did not stop because one horse became exhausted; another replaced it.

The Immortals did not cease to exist because one soldier died; another entered the ranks.

In both cases, continuity was the secret.

Today, more than 2,500 years later, we do not know the names of most of these soldiers. We cannot even answer every question about their organization with certainty.

Yet their collective name survives.

Perhaps in that sense, the soldiers Herodotus called the Immortals achieved exactly what their name promised.

Next Week: Xerxes — The King Who Led One of the Greatest Military Expeditions of the Ancient World.