ancient source-herodotus acount of the battle of thermophylae
modern source-300 the movie or the novel the lost army by valerio....
300?!! Never ever use a Hollywood movie as a source! My teacher did the HSC marking for Sparta and she was telling us how the markers laughed when somebody mentioned 300.
When you look at the ancient sources, you have the main writers accounting about Sparta - Plutarch, Xenophon, Aristotle, etc. Basically the people contributing to the Spartan mirage are non-Spartans, and they're usually pro-Sparta.
When you look at modern sources, you look at the scholarships - 1980s, 1990s, you have scholars questioning the traditional understanding of Sparta. Therefore it's difficult to get a true picture of Spartan society.
Spartan's militaristic nature directly contributes to the Spartan mirage. Sparta is seen in popular culture as an utopian, militaristic society. When you look at the army, you look at the gradual change of Sparta from the rest of the Greek states - how Spartan customs and values revolve around ideals of perfect warriors "hoplites".