When the invasion by Xerxes became imminent in 480 BCE, the city-states met in a council to determine their strategy. There were some difficulties they had to overcome: * First, Xerxes' agents had alread been through Greece in a softening up campaign, with bribes and promising dissident factions in the cities that they would become the rulers of their cities under his overall rule. The council was therefore unsure who was reliable and who had 'Medised', but certainly suspected cities such as the Thessalians and Thebes which would be the first to be run over by Xerxes' forces and therefore most likely to switch sides. * Second, Xerxes had a superior fleet (drawn from Phoenicia, the Greek cities of Asia Minor and the islands, and Egypt). This gave him the amphibious capability to attack any of the cities near the coast (which most were) one by one. So the cities were reluctant to send out their armies to a joint force against the invasion, but kept them at home to defend their cities. The states of the Peloponnese talked of building a wall across the Isthmus of Corinth, and sending some of their soldiers to man it, but this was a sham as the Persian fleet could simply outflank this and land soldiers directly at the cities, and the contingents would never actually be released from their cities. Athens knew it was exposed, and made plans to evacuate the city, sending the families to cities in the Peloponnese for sanctuary, with all its manpower, including its infantry, manning its 200 warships. Athens and Sparta sent an expeditionary force of 100 ships and 10,000 infantry north to the pass at Tempe to act as a delaying force and stiffen the resolve of the northern city-states. The king of Macedonia, who had no option but to side with Xerxes, sent secret word to them that Xerxes intended to bypass this by cutting an inland road, so this expedition was withdrawn. The plan was then resolved that the only way to free the southern cities to come out and fight was to destroy the Persian amphibious capability. As the Persian fleet was almost twice the size of the Greek one, and had larger ships, it was determined to arrange to engage it in narrow waters so that the Greeks would not be overwhelmed. The strait between the island of Euboea and the mainland was selected, and small forces sent from several of the cities to block the land route at the Thermopylae pass to force the Persians to send their fleet through the strait nearby to outflank the land blockage. The pass was held for three days, and on each day a naval engagement was fought, with the combined Greek fleet coming off second best. It was withdrawn to the Strait at Salamis for a second attempt there, which was successful. The Persian amphibious capacity was broken, and Xerxes could not even protect his sea supply line and had to take half his army home as the countryside could not support them over winter. As planned, no longer threatened by Persian amphibious attacks, the cities of the south joined their forces at Plataia the following spring and defeated the remaining half of Persian army and its Greek allies. At the same time the Greek fleet destroyed the rump of the Persian fleet at Mykale in Asia Minor.
By xerxis trying to take over the greek empire