In 480 BCE, the Persian Empire sent the largest army the ancient world had ever assembled to conquer Greece. King Xerxes brought, according to Herodotus, over a million soldiers, though modern estimates place the number closer to one hundred thousand to three hundred thousand. Either way, it was overwhelming. Greece was a collection of squabbling city-states with no unified army. The situation was, by any rational assessment, hopeless. Leonidas of Sparta took three hundred Spartans and walked to Thermopylae to hold a narrow mountain pass against the entire Persian army. He knew he was going to die.

The Pass Was the Strategy

Thermopylae means Hot Gates, named for the thermal springs nearby. The pass was narrow enough that the Persians could not use their numerical advantage. It did not matter if Xerxes had a million men or a hundred thousand. Only a few dozen could fight at a time in the compressed space between the mountains and the sea. Military historians at the Hellenic Army Academy have studied the Battle of Thermopylae as a masterclass in force multiplication through terrain. Leonidas chose the ground specifically because it negated everything the Persians were good at: cavalry, archery, and overwhelming numbers. In the pass, the fight was spear against spear, shield against shield, and the Spartans were the best infantry fighters in the ancient world. For two days, the Greeks held. The Persians sent wave after wave of soldiers into the pass and were thrown back each time. Xerxes reportedly sent his Immortals, the elite ten thousand, and they were repulsed as well. The three hundred Spartans, along with several thousand other Greek allies who are often forgotten in the retelling, fought with a discipline and ferocity that the Persians had never encountered.

He Stayed When Everyone Else Left

On the third day, a Greek traitor named Ephialtes showed the Persians a mountain path that led behind the Greek position. Leonidas learned of the betrayal and dismissed most of the Greek army. He kept his three hundred Spartans and a few hundred Thespians and Thebans. They would fight a rearguard action to buy time for the retreating Greeks. Scholars of ancient warfare at the University of Cambridge have debated why Leonidas stayed. The most compelling argument is that he was following a Delphic prophecy that said either Sparta would be destroyed or a Spartan king would die. By choosing death, he chose to save his city. It was a calculation, not a tantrum. The final stand was fought on open ground. The Greeks fought until their spears broke, then fought with swords, then fought with hands and teeth. According to Herodotus, they fought over the body of Leonidas himself after he fell, driving the Persians back four times before being overwhelmed. The Greeks lost the battle. They won the war. The delay at Thermopylae gave the Greek navy time to prepare for the Battle of Salamis, where the Persian fleet was destroyed. Xerxes retreated. Greece survived. Western civilization, for whatever that is worth, continued. Three hundred men held a pass. The math said it was pointless. The result said otherwise.