The one

At Thermopylae, the allied Greek nations deployed a small force of between four and seven thousand Greek heavy infantry against the invading Persian army of two million. Leading the Greeks was a force of three hundred Spartans, chosen by the fact that they were all "sires" - they were fathers to male children, which would preserve their bloodlines after what was likely a suicide mission.

Thermopylae was the only way into Greece for the Persian army, and presented the perfect choke point - a narrow pass bordered by a sheer mountain wall on one side and a cliff drop-off to the ocean on the other. This location decreased the advantage of the Persian's numerical superiority, and gave the Greek allies enough time to ready a larger, main force to defend against the Persians.

Though Xeones is critically wounded in the battle, the Persian King Xerxes orders his surgeons to make every effort to keep the captive squire alive. The book is Xeones' relation of the battle and events leading up to it to Xerxes and his royal scribe as the Persian army advances toward Athens.

Much of the narrative explores Spartan society, the agoge, which is the military training program which all Spartan boys must complete to become citizens or Peers. The novel also details the heroics of several dozen Spartans, including their king, Leonidas, the Olympic champion Polynikes, a young Spartan warrior named Alexandros, and the Spartan officer Dienekes. Pressfield employs detailed descriptions of the Spartan phalanx in battle, as well as the superior training and discipline of the Spartan warriors

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