Persia was an expanding power, and had taken over several Ionian Greek cities in present day Turkey. These cities revolted with the encouragement and support of Athens. The Persian king Darius decided to punish Athens, but was defeated at Marathon. His son Xerxes invaded Greece with an army of 150,000 men and a navy of 600 ships. He finally defeated the Spartans at Thermopylae, and burned Athens, but was defeated by the Athenian navy at Salamis, and returned defeated to Persia. -Credits to the rightful owner from Yahoo-