At the heart of the Persian army were the “Immortals,” an elite regiment of 10,000 infantrymen whose numbers never changed. It’s estimated that King Darius III of Persia was in command of a total of 2.5 million soldiers spread across his vast empire. Whether motivated by Greek pride or the spoils of imperial conquest, Alexander picked up where his father left off and marched into Persia in 334 BC, where his army of 50,000 would be tested against the largest and best-trained fighting force in the known world. “He’s invading Persia to punish the Persians retroactively for daring to invade Greece in the first place.” “Alexander creates a propaganda campaign that the Macedonians are invading Persia on behalf of the Greeks, even though Macedon wasn’t part of Greece and didn’t fight on the side of Greece in the original Greco-Persian wars,” says Wrightson. That conflict featured the famous Battle of Thermopylae, where 300 Spartan warriors made a heroic last stand against tens of thousands of Persian invaders. So as he turned his attention back to Persia, Alexander framed his campaign against the Achaemenid Empire as a patriotic retaliation for Persia’s failed invasion of the Greek mainland a century earlier. Always the savvy strategist, Alexander knew that he couldn’t rule the Greek mainland by fear and brute force alone.
