His reign divided the empire into provinces governed by satraps, allowing each province its own government while maintaining some centralizing authority. He developed commerce, building a network of roads, exploring the Indus valley, and connecting the Nile with the Red Sea by canal. After suppressing a revolt of the Greek cities in Ionia (499–494 bc), he invaded Greece to punish the mainland Greeks for their interference, but was defeated at Marathon (490 bc).