“third Persian expedition”? Darius was first, Junior (Xerxes) was next. What’s this “third” stuff? Maybe I remember incorrectly.
The first was when the Persian fleet was destroyed in a storm, and the second was the Greek victory at Marathon in 490 BC. The expedition which included Thermopylae was the third, according to this reckoning; it’s valid, though, to leave out the first of these, since the fleet was destroyed prior to any battle.