A Gap You Could Not Widen

Thermopylae in 480 BC was a track between cliff and sea narrow enough that a cart could barely pass — Herodotus says a single wagon's width at the tightest point. That single fact is the campaign. Persian numerical superiority, whatever it actually was, cannot be applied in a corridor where only a few men can reach the front at once, and where a long spear and a heavy shield in close order beat a lighter-armed soldier who cannot be flanked or supported. Leonidas did not bring enough men to win a battle. He brought enough men to fill a gap, and held the gap the allies had chosen, one that could not be made bigger.