If you’ve seen the movie 300, you’ll know the drill: 300 Spartan warriors (and a few thousand allies) holding off the massive Persian army at a narrow mountain pass. The Battle of Thermopylae in 480 BC is a textbook example of  “against all odds” — the Spartans knew they were outnumbered, but they held the line for three days, showing unmatched bravery and iron discipline.  

The narrow pass gave the vastly outnumbered Greek forces a strategic advantage, funnelling the Persian forces into a tight space where their numbers counted for less. The Persians only broke through after a local Greek traitor, Ephialtes, revealed a secret path that allowed them to flank the defenders. Even knowing they were doomed, Leonidas and his men fought to the last, choosing a heroic death over retreat.