Experts illuminate the brutal standoff at the "Gates of Fire," when 300 Spartans held off the Persian army. On one side was a vast army assembled by the Persians to avenge their defeat at Marathon. On the other were 300 Spartan soldiers, the most celebrated warriors of ancient Greece. For over a weak, this tiny force defied the odds and held a narrow mountain pass. Though they died to the last man, it was one of the greatest displays of military heroism in history.