(i) The second Persian invasion of Greece was catalysed by the spectacular failure of the first, with the then Persian King Darius. I seeing his desire to subjugate the city-states of Athens and Eretria end brutally at the Battle of Marathon in 490 BCE.
(ii) Indeed, despite sending over 300,000 soldiers to take down the Persian's western enemy, the majority of Greece - and certainly the mainland - remained firmly out of Persian hands, with Darius himself checked in his empire's expansion for the first time.
(iii) Well, if you were a Spartan, the most war loving, brutal and savage city-state in the entirety of Greece, then you would fight - and you would do so to the last man.
(iv) That is exactly what King Leonidas I of Sparta did in 480 BCE and, despite falling in battle, he fell a free man on his home country's soil and helped repel the Persians from mainland Greece once and for all.
(v) After receiving the news of the defeat, however, his will remained intact and he began preparations for an even larger second invasion.