well, since you asked
the same time the hellenic alliance was defending thermopylae, the greek navy (led i think by the athenians) attacked xerxes fleet off the coast of artemisium. he got owned fairly badly. but when news of the defeat on land reached the ships, they decided to scoot off back to athens.
they parked themselves off the island of salamis, which is very close to the athenian port, and evacuated the population of athens onto that island. xerxes's army marched down and in a few weeks razed empty athens to the ground.
in the meantime the hellenic armies were building a defensive wall at the isthmus near corinth to prevent the persians from getting into the peloponnese. the navy was stuck at salamis and couldn't decide whether they should make a stand against xerxes's navy where they were or whether they should retreat to the isthmus and fight alongside the armies. in the end xerxes made a mistake and ordered his navy to attack the greek fleet where they were. because of the narrow straights between the coast of salamis and athens the greeks with their heavier ships and better seamen completely crushed xerxes's navy, which was i think about 1,200 triremes. the greeks only had 380.
this was a mistake, had xerxes the wit to listen to one of his advisors he could have sent his fleet south to attack sparta and the peloponnese from the other end rendering the defensive works at the isthmus useless. as it is, his navy was destroyed as he looked on from the ruins of athens. the loss of his navy was such a shock to him he gave up the idea of conquering greece as a bad job. he took the majority of his army and headed home, leaving behind 300,000 troops under the command of his general mardonius who promised to deliver greece to xerxes on a platter, or something.
winter passed, and the persian army spent their time in the boeotian city of thebes. in the meanwhile, the fortification of the isthmus was completed and the spartans reneged on their agreement with the athenians to attack the persians. only when the athenians threatened to ally with the persians did the spartans send their army forth.
the hellenic alliance fought the persians at a place called plataea, close to the city of thebes. about 90,000 greeks fought against 300,000 persians. the persians were all wiped out and the greeks had a great time plundering the gold and wealth the idiotic persians had brought with them.
after the battle of plataea the greeks sieged the city of thebes. serves them right, the traitors. not every greek city was part of the hellenic alliance. some surrendered to xerxes; others indeed went to him with open arms.
soon after the battle against persia, sparta and corinth declared war on athens, bringing greece back to her usual petty squabbles and tribal ways.
