"On the third day, Leonidas led his 300 Spartan hoplites (elite troops selected because they had living sons back home) plus the allied Thespians and Thebans against Xerxes and his army of "10,000 Immortals." (Not ONE MILLION)"
This is a mistake. The Immortals were an elite force within the larger contingent variously estimated from some hundreds of thousands and as many as two million men. Xerxes drew troops from all over his empire, which, at the time stretched from Asia minor to India and to Egypt as well, so it is not beyond possibility for him to raise an enourmous force. The Immortals were essentially the palace gaurd, consisting of fanatically loyal and superbly trained soldiers. It was these that the 300 Spartans met with Leonidas and defeated. Only the betrayal of a Greek, giving away the secret of a pass that enabled Xerxes to encircle Leonidas, brought about the ultimate slaughter of the 300.
4 thousand here from Pelop's land
Against 3 million once did stand
The Spartans have a special epitaph; it runs
Go tell the Spartans you who read:
We took their orders and are dead.
Military historians call this maneuver "The Jon Kerry."