How Many Persians?

The Persian army under Xerxes was huge, but it probably numbered around 70,000-300,000 — not the millions Herodotus claimed. Still overwhelming, yet the narrow coastal pass at Thermopylae cancelled out Persia's advantage in numbers.

When the end became certain, Leonidas dismissed most of the allied force, keeping the Spartans, Thespians, and Thebans to cover the retreat. The Spartans and Thespians fought to the death; the Theban contingent is more complicated, with ancient sources reporting that many surrendered. The battle was a defeat on paper, but it bought Athens the time it desperately needed.