He married Gorgo, daughter of his adoptive brother Cleomenes I, with whom he had a son, Pleistarchus.  In 480 B.C.E.  he commanded the defense of the isthmus of Thermopylae, leading 300 Spartans and several thousand soldiers from other Greek states.  For three days, he repulsed the attacks of the many-thousand-strong army of the king of Persia. He and 300 hundred Spartans were defeated but their sacrifice gave Greece enough time to win the war. 