It is a great moment in history.
When the Persians were about to attack Greece, the Spartans, led by King Leonidas and 300 men, kept the entire 100,000 Persian army bottled up in a mountain pass for two days while the Athenians mustered their army and navy to meet the Persians in battle. King Leonidas and all his men were eventually all killed, by the two days rallied the Greeks and they defeated the Persians at Battle of Marathon.
Actually, I got that wrong.
The Battle of Marathon happened in 390 BC, and Leonidas stopped the second Persian attempt at the Battle of Thermopylae in 480 BC. In both cases, though, the Persians lost, even though they had a 10 to 1 man advantage over the Greeks!
Classical historians put the total number Greeks present for most of the battle at about 7,400. No doubt the 300 - King Leonidas’s bodyguard was the core the army was built around. Classical historians say 700 Thespians (No not actors & actresses! Hoplites from Thespiae) - led by Demophilius stayed and died also. Classical historians have an upper number for the Persians at 2.6M, modern historians place it at 120K to 300K. So a 1000 stayed and fought a rear guard that save 5K to 6K to fight again at Platea. Still a story that inspires us all.
https://en.wikipedia.org/wiki/Battle_of_Thermopylae