Xerxes I assembled the largest invasion force the ancient world had ever seen — over a million men by Herodotus’s count — to avenge his father Darius’s defeat at Marathon and conquer Greece once and for all. He bridged the Hellespont, whipped the sea for disobedience, and burned Athens to the ground. Then he lost the war, retreated to Persia, and was assassinated in his own bedchamber by his bodyguard.

This episode traces Xerxes from his succession struggles through the massive Greek invasion, the battles of Thermopylae and Salamis, and the palace conspiracy that ended his reign in blood.

• Xerxes’s succession to the Persian throne and his decision to finish his father’s war with Greece
• The massive engineering feats — bridging the Hellespont, cutting the Athos canal
• The battles of Thermopylae and Salamis that turned the tide against Persia
• The palace conspiracy and assassination that ended the reign of the King of Kings