What is the story about the 300?
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.
https://www.ancient.eu/Persian_Wars/
The Persian Wars refers to the conflict between Greece and Persia in the 5th century BCE which involved two invasions by the latter in 490 and 480 BCE.
Several of the most famous and significant battles in history were fought during the Wars, these were at Marathon, Thermopylae, Salamis, and Plataea, all of which would become legendary.
The Greeks were, ultimately, victorious and their civilization preserved.
If they had been defeated then the western world may not have inherited from them such lasting cultural contributions as democracy, classical architecture and sculpture, theater, and the Olympic Games.
King Xerxes continued his predecessor Darius’ vision, and in 480 BCE he gathered a huge invasion force to attack Greece again, this time via the pass at Thermopylae on the east coast.
In August 480 BCE a small band of Greeks led by Spartan King Leonidas held the pass for three days but were killed to a man. (the 300)
At the same time, the Greek fleet managed to hold off the Persians at the indecisive naval battle at Artemision. Together, these battles bought Greece time and allowed for its cities to steel themselves for the bigger challenges yet to come.