[Illustration: THE VALE OF TEMPE. [_To face page_ 231. ] The expedition to North Thessaly was made under a gross misapprehension as to the geography of the region. The Greeks who despatched it were evidently under the impression that the Tempe pass was the only practicable entrance into that country. It will be best to speak in detail of the passes of this region when the march of Xerxes is described; for the present suffice it to say that in Tempe itself there is on the hills north of the Peneius River a path by which the defence of the main road, which keeps on the south bank of the stream, may be turned; and, furthermore, there are two other passes through the Olympo-Cambunian chain, by which entrance may be obtained into the Thessalian plain. The army, of which the Lacedæmonian contingent was commanded by Evænetos,[103] and the Athenian by Themistocles, found itself in a false position. It says something for Herodotus’ military insight that, although he gives what was, so he says, the generally received story, that the retreat was decided upon in consequence of a message from Alexander, a Macedonian, describing the enormous numbers of the Persian army, he believes the real reason to have been the discovery that the Tempe defile could be turned by other passes. The growth of sea communication, and the consequent disuse of some of the old land routes, probably accounts for the ignorance which the Greeks displayed of a region through which the old trade route to the north must have passed. The army returned to its ships at Halos, and so home. Then, says Herodotus, the Thessalians, abandoned by their allies, readily took part with the king. That the Locrians of the East were among those who gave earth and water is not surprising. Though within the gates of Thermopylæ, their country was north of the Œta range. It was imperatively necessary that, in case they were deserted, they should be in a position to make terms with the invader; for the flood of invasion, unless stemmed, must pass in full stream their way. The length of their narrow territory was traversed by the great military highway from the North. The fiasco of the expedition to Tempe had no doubt discouraged the northern Greeks, and among the powers represented at the Isthmus it must have told greatly in favour of the Peloponnesian strategy. Be that as it may, the design of the Council at the Isthmus was to make the defence a Panhellenic effort, and to persuade the whole Greek world to lend a helping hand towards the preservation of the mother country. It may be suspected that Athens roused and sustained the energy which such an effort implied; but the official invitations sent out appealing for assistance were evidently issued in the name of the Congress as a body.[104]