Long before Hollywood made him an icon, Leonidas I was a Spartan middle son buried deep in a messy line of succession. This episode looks past the pop-culture myth to the man himself: a royal who was put through the brutal agoge, the Ephors who could order a king to take a second wife, and the family feud that eventually put Leonidas on the Agiad throne around 489 BC.

We then follow him to the narrow pass of Thermopylae in 480 BC. The Oracle at Delphi had given him a grim prophecy, and the Carneia festival limited how many troops Sparta would send, so he faced Xerxes’ huge Persian army with only 300 Spartan hoplites and a small allied force. We look at why he stayed after Ephialtes betrayed the mountain path, how he was honored in Sparta after his death, and how a military defeat turned into a lasting ideological victory.

• How the Agiad succession crisis and the Ephors’ intervention set up Leonidas’s unlikely rise to the throne
• Why going through the agoge earned Leonidas the respect of his soldiers and of the wider Greek coalition
• The Delphic prophecy, the Carneia festival, and why Sparta sent only 300 hoplites
• How the phalanx and the 50-foot-wide pass held off the Persians and the Immortals until Ephialtes revealed the goat path
• The Thespians who volunteered to stay, the Leonideia festival, and Leonidas’s legacy as the model of the defiant underdog