The long, narrow, and winding defile of Tempê, formed then, and forms still, the single entrance, open throughout winter as well as summer, from lower or maritime Macedonia into Thessaly: the lofty mountain precipices approach so closely as to leave hardly room enough in some places for a road: it is thus eminently defensible, and a few resolute men would be sufficient to arrest in it the progress of the most numerous host.[121] But the Greeks soon discovered that the position was such as they could not hold,—first, because the powerful fleet of Xerxes would be able to land troops in their rear; secondly, because there was also a second entrance passable in summer, from upper Macedonia into Thessaly, by the mountain-passes over the range of Olympus; an entrance which traversed the country of the Perrhæbians and came into Thessaly near Gonnus, about the spot where the defile of Tempê begins to narrow. It was in fact by this second pass, evading the insurmountable difficulties of Tempê, that the advancing march of the Persians was destined to be made, under the auspices of Alexander, king of Macedon, tributary to them, and active in their service; who sent a communication of this fact to the Greeks at Tempê, admonishing them that they would be trodden under foot by the countless host approaching, and urging them to renounce their hopeless position.[122] This Macedonian prince passed for a friend, and probably believed himself to be acting as such in dissuading the Greeks from unavailing resistance to Persia: but he was in reality a very dangerous mediator; and as such the Spartans had good reason to dread him, in a second intervention of which we shall hear more hereafter.[123] On the present occasion, the Grecian commanders were quite ignorant of the existence of any other entrance into Thessaly, besides Tempê, until their arrival in that region. Perhaps it might have been possible to defend both entrances at once, and considering the immense importance of arresting the march of the Persians at the frontiers of Hellas, the attempt would have been worth some risk. So great was the alarm, however, produced by the unexpected discovery, justifying, or seeming to justify, the friendly advice of Alexander, that they remained only a few days at Tempê, then at once retired back to their ships, and returned by sea to the isthmus of Corinth,—about the time when Xerxes was crossing the Hellespont.[124] [121] Herodot. vii, 172. τὴν ἐσβολὴν τὴν Ὀλυμπικήν. See the description and plan of Tempê in Dr. Clarke’s Travels, vol. iv, ch. ix, p. 280; and the Dissertation of Kriegk, in which all the facts about this interesting defile are collected and compared (Das Thessalische Tempe. Frankfort, 1834).