The Immortals presence at the battle of Plataea is based on Herodotus' description of Mardonius selecting troops for his army while in Thessaly. (Herodotus -The Histories, 8, 113)

"he chose the troops which were to serve under his command: these were, first, the Persian regiment of Immortals"

The following points show that the presence of the Persian Immortals at the battle of Plataea in 479 B.C. is far from certain and possibly unlikely.

1. The battle of Plataea happened at least six months after Mardonius took command of the Persian army in Greece and Herodotus described how much was to happen within that time.
2. The Immortals were the elite of the Persian army and from our knowledge had previously only campaigned with the King.
3. Xerxes was concerned not just for his own safety but also for that of the empire. With the naval defeat at Salamis as a possible trigger to rebellion within the empire, Xerxes had more than the Greeks to worry about. Ionia and Babylon both were possible trouble spots but Xerxes could have easily faced a widescale rebellion similar to that his father Darius faced when he first took the throne. Xerxes now needed his Immortals far more than Mardonius. He could not afford to be seen to have lost both his fleet and his army.

4. There is no specific reference to the Immortals at Plataea despite Herodotus giving fairly detailed descriptions of the troops which were present. Considering that he mentions them several times during campaign, it is quite possible he was not sure about their presence or else he wanted his readers to continue to believe that the Greeks had defeated the best of the Persian army.
5. Xerxes was keen, not to 'lose face'. Artemisia advised Xerxes that the Greeks would achieve "poor triumph" if they defeated Mardonius. Xerxes on the other hand could return home having accomplished his revenge on Athens.

   "And even if things go wrong with him, it will be no great matter, so long as you yourself are safe and no danger threatens anything that concerns your house. While you and yours survive,.." (Herodotus -The Histories, 8, 102)

6. Herodotus described the Persians at Plataea as fighting 'disordered', in groups of five to ten or individually, they would break formation and attack the Greeks. This is not the behaviour that we expect from trained professional troops and certainly not from the King's elite troops.
7. Herodotus said that Hydarnes, the commander of the Immortals throughout the whole expedition, was unwilling to leave the King and returned to Asia with Xerxes.
8. Artabazus (Herodotus -The Histories, 8, 125), escorted Xerxes to the Hellespont with 60,000 of Mardonius' 'picked troops'. It is likely the Immortals were amongst those chosen for this task.
   If we consider they were chosen to escort the King, it could then be possible the Immortals left Artabazus once they reached the Hellespont and continued with Xerxes to Sardis. However if they did remain with Artabazus, their fate is still uncertain considering the events that were to take place.

   After escorting Xerxes back to Asia, Artabazus started the return march to rejoin Mardonius only to find that several towns on the Pallene peninsula had rebelled against Perian authority after learning of the Persian naval defeat at Salamis. Artabazus was not in a hurry to rejoin Mardonius who he was wintering in Thessaly and Macedonia, so layed siege to the towns of Potidaea and Olynthus. Olynthus soon fell but Potidea still held out. Three months into the seige there was an exceptionally low tide which Artabazus saw as an opportunity to move his troops to surrond the town. During the move however, his troops were caught by the rising waters and many were drowned. The Potideans took full advantage of the situation and came out in boats to attack the Persians. Herodotus says the Persians loss was heavy and Artabazus was forced to call off the siege and rejoin Mardonius.
   Considering the likelihood of the Immortals being part of the 60,000 picked troops under Artabazus' command, there is the possiblility that they were the ones who were caught by the rising waters.

   • As with their flank march at Thermopylae, the Immortals were likely to be the ones to lead the march around the city.
   • The Potideans recognised the troops caught in the rising waters as the ones who had desecrated the shrine of Poseidon. The Immortals would be the most recognisable troops in the army.
   • The loss was considerable as Artabazus returned to Greece after this incident.
   • Although initially assigned 60,000 troops on his march to the Hellespont, Artabazus had only 40,000 troops under his command at the Battle of Plataea. This suggests a possible loss of 20,000 troops, assuming there was no reorganisation when he reached Plataea.

The Immortals were not just merely an elite Persian regiment but were a key instrument of Persian imperial power. They symbolised both Persian superiority and the power of the King and were indispensable to the King's authority over a vast, recently subjected and often rebellious empire. Returnining to his capital without them, particularly after the naval defeat at Salamis was "so unlikely as to be considered a fantasy in the absence of definite proof".(Gunther. Nov, 2002)

In summary, it is not possible to come to any definite conclusion about the fate of the 'Immortals' after Salamis. We can only consider the possibilities and continue to look for the undiscovered. The following list is a summary of those possibilities.
The Immortals;

• were placed under Mardonius' command and fought at Plataea as generally believed.
• returned to Sardis with Xerxes under the command of Hydarnes.
• escorted Xerxes back to the Hellespont under the command of Artabazus and then continued to Sardis with Xerxes.
• escorted Xerxes back to the Hellespont, then remained with Artabazus only to be decimated at the siege of Potidaea.
• returned with Artabazus to Plataea and were reorganised back under Mardonius' command.

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