Thermopylai and the Sparta hype that rose after it are hideously overrated. I commend to your attention AskHistorians Podcast 116, featuring our own u/Iphikrates, which focuses specifically on Thermopylai and in particular the Zack Snyder movie. If you want to learn more than you ever thought you'd want to know about Ancient Greek warfare, I highly recommend browsing through his flair profile.