128. Then Xerxes seeing from Therma the mountains of Thessaly, Olympos and Ossa, that they were of very great height, and being informed that in the midst between them there was a narrow channel, through which flows the Peneios, and hearing also that by this way there was a good road leading to Thessaly, formed a desire to sail thither and look at the outlet of the Peneios, because he was meaning to march by the upper road, through the land of the Macedonians who dwell inland, until he came to the Perraibians, passing by the city of Gonnos; for by this way he was informed that it was safest to go. And having formed this desire, so also he proceeded to do; that is, he embarked in a Sidonian ship, the same in which he used always to embark when he wished to do anything of this kind, and he displayed a signal for the others to put out to sea also, leaving there the land-army. Then when Xerxes had looked at the outlet of the Peneios, he was possessed by great wonder, and summoning his guides he asked them whether it was possible to turn the river aside and bring it out to the sea by another way. 129. Now it is said that Thessaly was in old time a lake, being enclosed on all sides by very lofty mountains: for the parts of it which lie towards the East are shut in by the ranges of Pelion and Ossa, which join one another in their lower slopes, the parts towards the North Wind by Olympos, those towards the West by Pindos and those towards the mid-day and the South Wind by Othrys; and the region in the midst, between these mountains which have been named, is Thessaly, forming as it were a hollow. Whereas then many rivers flow into it and among them these five of most note, namely Peneios, Apidanos, Onochonos, Enipeus and Pamisos, these, which collect their waters from the mountains that enclose Thessaly round, and flow into this plain, with names separate each one, having their outflow into the sea by one channel and that a narrow one, first mingling their waters all together in one and the same stream; and so soon as they are mingled together, from that point onwards the Peneios prevails with its name over the rest and causes the others to lose their separate names. And it is said that in ancient time, there not being yet this channel and outflow between the mountains, these rivers, and besides these rivers the lake Boibeïs also, had no names as they have now, but by their waters they made Thessaly to be all sea. The Thessalians themselves say that Poseidon made the channel through which the Peneios flows; and reasonably they report it thus, because whosoever believes that it is Poseidon who shakes the Earth and that the partings asunder produced by earthquake are the work of this god, would say, if he saw this, that it was made by Poseidon; for the parting asunder of the mountains is the work of an earthquake, as is evident to me.