The Persian Immortals: the feared elite guard of the Achaemenid empire

When were they first established?

The Immortals are understood to have been originally assembled following the capture of Babylon in 539 BC. The female commander Pantea Arteshbod, believed to have been appointed to govern Babylon under Cyrus’ rule, is thought to have been the architect of the Immortals, establishing them as an elite guard. A counter claim comes from Xenophon, who – in Cyropaedia, his partly fictional biography of Cyrus – declares that it was Cyrus himself who constructed a palace guard from the most fearsome soldiers in his standing army, the spada.

How were Immortals chosen?

The Immortals largely consisted of Persians, although a fair smattering of Medes and Elamites were assimilated into their ranks, their mere presence showing that Cyrus was unafraid to give his former enemies positions of high responsibility. With the spada required to provide their own military equipment, they – and thus the Immortals too – represented the wealthier portion of Achaemenid society.

Young boys were trained from the age of five to become members of the spada, being taught how to ride horses, fire arrows, hunt and live off the land. They became soldiers at the age of 20 and, after a life that almost certainly saw plenty of conflict, were allowed to retire when they reached 50, whereupon they were granted a pension and land rights. The very best soldiers in terms of combat ability and character – believed to be around the top tenth of the spada – were anointed as Immortals.

Where did the name 'Immortals' come from?

According to the historian Herodotus, the Immortals were precisely 10,000 strong, and it’s the maintenance of this number that led to their name. Every time an Immortal was killed, seriously wounded, taken ill or retired, they were immediately replaced, thus making them appear unstoppable. They also instantly removed their dead from the battlefield. With no corpses on show to their enemies, the practice offered the illusion that these much-eulogised soldiers were not mere mortals.

What weapons did the Immortals carry?

The main weapon used by the Immortals was a spear – six feet long and boasting a seriously sharp spearhead. On the other end of the spear was a counterbalance that, when used as a blunt weapon to strike an enemy soldier, could be just as deadly.

The counterbalances took the shape of fruit; the most prestigious was apple-shaped, as this denoted its owner to be one of the 1,000 most elite members of the Immortals. These bodyguards of the emperor were known as ‘apple-bearers’ and their spears were longer, too. The Immortals also carried a number of small weapons, including a sagaris – a battle-axe that was light enough to be used one-handed.

What did they wear?

As far as it’s known, the Immortals didn’t pay too much attention to headwear. They wore ‘tiaras’, which took differing forms according to various accounts. Sometimes these tiaras are described as felt caps, which covered the face and kept wind and dirt at bay; at other times, the headgear is said to have been merely a headdress made of cloth. Their body armour consisted of overlapping plates of bronze and iron, protection that looked not unlike the scales of a fish. They also carried hefty, leather-covered shields of wicker and wood.

The Immortals’ infantry would march in support of the archers who took the front in battle, with cavalry at the side. With the skies dark and thousands of arrows in flight, they would have looked a fearsome sight. With the Immortals’ breastplates flashing in the sunlight, many cities simply surrendered when they first saw them approach.

Just how elite were this elite band?

Evidence of the high regard in which the Immortals were held in comes from another observation from Herodotus. His writings report that not only were these 10,000 men “conspicuous for the huge amount of gold they wore about their persons”, but they also indulged when it came to their lifestyles.

Herodotus explains that, whenever the Immortals were travelling, “they also brought covered wagons for their concubines, sizeable and well-equipped retinues of slaves, and their own personal provisions, separate from those of the other soldiers, transported by camels and yoke-animals”.

How successful were the Immortals as a fighting unit?

After Cyrus’ death in 530 BC, the Immortals were retained by his successors across the lifespan of the Achaemenid empire, including his son Cambyses II (who conquered Egypt) and Darius the Great. It is widely assumed that Darius deployed his elite brigade when he invaded Greece, but the Immortals’ presence couldn’t stop his defeat at the battle of Marathon in 490 BC.

The battle that the Immortals have been most identified with came 10 years after Marathon, following Xerxes I’s widescale invasion of Greece in retaliation for his predecessor’s defeat.

At the pass of Thermopylae, Xerxes’ regular troops – mainly consisting of Medes and Cissians – encountered stiff resistance from the outnumbered Spartans. Spartan general Leonidas I had galvanised his modest 300-strong Spartan elite force to the extent that they didn’t just repel Xerxes’ men, but forced them back. Xerxes’ plan B was to send his Immortals in against the pugnacious Spartans.

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As Herodotus chronicled, “it was expected that they would easily finish the job, but when they came to engage the Greeks, they were no more successful than the Medes had been”.

Their inferior weaponry was quite probably the reason why they hadn’t cut through the comparatively light Spartan ranks. As Cyrus made territorial gains to expand his empire, those he faced used the same weapons and wore the same armour as his own troops, meaning the superior fighting skills of the Persians were the deciding factor. By the time of Xerxes’ rule, though, the Spartans boasted more advanced weaponry and protection, as the emperor would discover again at other focal points of his invasion of Greece, in particular at the battle of Plataea in 479 BC.

How long did the Immortals last as a unit?

Despite their notable defeats, the Immortals would stay in operation as the elite unit throughout the remainder of the Achaemenid empire – all the way until the battle of Gaugamela in 331 BC, when they came up against the Macedonian forces of Alexander the Great. The Achaemenid defeat to Alexander signalled the end of that particular empire – but it wasn’t necessarily the end of the Immortals.

Alexander was a deep admirer of Cyrus and chose to retain an elite force of Persian soldiers as part of the protective shield surrounding his courtroom. The author Polyaenus would later write of “10,000 Persians, the handsomest and tallest of them, adorned with Persian decorations and all carrying short swords”. After Alexander’s death in 323 BC, his empire was divided four ways.

The portion of his empire that covered central Asia and Mesopotamia was handed to Seleucus I who established the Seleucid empire, but it remains unclear whether he maintained the tradition of having this elite band of fighting men offering an imperial guard.

But the influence of the Immortals didn’t die when they disbanded. When the Sasanian empire – the last-ever Persian imperial dynasty before Muslim control of the region in the 7th century – was established in AD 224, it too instituted a system of elite soldiers, also known as the Immortals.

This content first appeared in the December 2021 issue of BBC History Revealed