The first thing the Greeks did was to hold a conference at Corinth, which was attended by envoys from all the leading states except Argos and Thebes, which stood aloof. At this conference the Greeks made three important decisions. They resolved that they would reconcile all their own differences and bring to an end the wars they had with one another; as Hellenes they would unite against the common foe. Then they determined to send spies to Asia, who should bring back accurate reports of the preparations and power of Xerxes. And lastly, they would send messengers to the colonies in Sicily, Corcyra and Crete asking for assistance.
Three spies set out, but they were captured in Sardis and condemned to death. When Xerxes, however, heard what had happened, he sent for the spies, who were brought into his presence. To their surprise, instead of being led out to immediate execution, Xerxes commanded that they should be led round and shown the whole army, both foot and horse, and when they had seen everything, they were to be set free to return home. He did this, because he said that
if the spies had been put to death, the Hellenes would not have been informed of his power, how far beyond any description it was; while on the other hand by putting to death three men, they would not very greatly damage the enemy; but when these returned back to Hellas, he thought it likely that the Hellenes, hearing of his power, would deliver up their freedom to him themselves, before the expedition took place, and thus there would be no need for them to have the labour of marching an army against them.
Little did Xerxes know the kind of freedom-loving people with whom he had to deal. So the spies looked at everything and then returned to Greece.
Meanwhile the messengers to the colonies returned. The answers to the appeal for support were very disappointing. Neither Sicily, Corcyra nor Crete would help. They either refused outright or made uncertain answers. They seem to have thought more of their own preservation than of the safety of Greece as a whole; they thought the Persian would probably win, and they preferred either to be on the winning side, or to be in such a position that they could make good terms with the Persian, did he conquer.
The Greeks now made ready to go out with their armies to meet the Persian foe. The chief command was given to Sparta, the greatest military state in Greece, and they marched to the Vale of Tempe in the north of Thessaly, where they hoped to meet Xerxes and prevent him from coming into Greece. When they got there, however, they found that it would not be possible to hold the pass against the enemy, for it was so situated that the Persians could attack them by sea as well as by land, and there was another path over the mountains by which the Persians could attack them in the rear. So the Greeks withdrew to Corinth, in order to deliberate further where they would meet the enemy. This retreat from Thessaly took place while Xerxes and his army were crossing the Hellespont, and it had important consequences for the Persians, for the Thessalians, hitherto never very loyal to Greece, seeing the other Greeks leave their land, "took the side of the Medes with a good will and no longer half-heartedly, so that in the course of events they proved very serviceable to the King."
The Greeks now decided on making a stand much further south at Thermopylae. This was a narrow pass and easier to defend, so they resolved
to guard it and not permit the Barbarian to go by into Hellas, and they resolved that the fleet should sail to Artemisium, for these points are near to one another, so that each division of their forces could have information of what was happening to the other.
At Thermopylae the Greeks awaited the Persians.