When Xerxes saw from Therma the very great height of the Thessalian mountains Olympus and Ossa and learned that the Peneus flows through them in a narrow pass, which was the way that led into Thessaly, he desired to view the mouth of the Peneus because he intended to march by the upper road through the highland people of Macedonia to the country of the Perrhaebi and the town of Gonnus; this, it was told him, was the safest way. He did exactly as he desired. He embarked on a Sidonian ship which he always used when he had some such business in hand, and hoisted his signal for the rest also to put out to sea, leaving his land army where it was. Great wonder took him when he came and viewed the mouth of the Peneus, and calling his guides, he asked them if it were possible to turn the river from its course and lead it into the sea by another way.