Why Thermopylae Worked

The pass was only about 15 meters wide at its narrowest point, and that was the whole secret — the Persians could not outflank the Greeks or bring their numbers to bear.

• First waves — Greek hoplites in a tight phalanx cut down the Medes and Cissians sent against them
• The Immortals — Xerxes then committed his elite guard of 10,000, and the Greeks broke them too
• The phalanx — overlapping shields and long spears were perfect for the cramped terrain

Ancient sources say Xerxes leapt from his throne three times in shock as his best troops were thrown back. And the defenders were not Spartans alone: several thousand allied Greeks from other city-states fought beside them.