Darius appointed Mardonius as one of his generals and, after the Ionian Revolt, sent him in 492 BC to punish the Greek city-state of Athens for assisting the Ionians. On his way to Athens, he used his army in the Ionian cities to depose the Greek tyrants and set up democratic governments, an action which surprised the Greeks at that time. Historians consider that he may have taken this action so that the Ionians would not revolt a second time after the Persian army had passed through. His fleet and army then passed across the Hellespont.