During the rule of Xerxes the Persian Empire was at its height in power. The newly conquered territories of the western coast of Asia Minor and Egypt, with their combined wealth, added to the magnificence of the already vast Persian empire. It was in fact the conquering of the west coast of Asia minor which put the city-states of Greece, primarily Athens, in conflict with the huge Persian war machine. The ionic states which were formally Greek colonies rose up against being ruled by the Persian empire in the ionic revolt of 499 BC. They pleaded with Athens for support in the war, to which Athens agreed because they sympathized with their Greek cousins, and also had the underlying fear Greece could be next. However, the revolt was put down in 494 and the Persian king of the time Darius sought retribution for Athenian interference. He sent an army to the north of the Aegean to conquer the lands into Greece and then Greece itself. However only Thrace, Thasos, and Macedonia were conquered and the Persian army subsequently was defeated at the famous battle of Marathon. Picking up where Darius left off Xerxes would eventually amass a force so great that none but the Persian empire could have levied it. Xerxes had learned from the former king's failure and "Marathon had shown the Persians that an attack on Greece in order to be successful, must be organized on a larger scale than any expedition which could be put on board a fleet" . The Persians sent a huge land force and navy which " was transported successfully over such a distance that it bears eloquent testimony to the military organization of the empire which dispatched it" . The numbers were staggering, Herodotus estimated the army to be over a million, but modern estimates place that figure at around 500,000. This force still outnumbered the Athenian army and that of its allies five to one. The allied navy was similarly dwarfed, in large part by Greeks who were either conquered by Persia or defected to the Persian side, they would contribute 400 ships to the Persian navy tipping the scales greatly in Persia's favor.