H. vii. 110, 111.
But, though he says that two of the Persian divisions took inland courses, he gives no real indication of what they were, though the mention of the Satræ and the description of their country suggests that one at least of these routes went near the higher peaks of Rhodope. THE EXPEDITION AT THERMA. It is, indeed, impossible on the practical question of physical and military possibilities, if Herodotus is right in his assertion with regard to this inland line of advance, to identify it with any other than a route leading to the sources of the Hebros, and then southward down the Axios or Strymon valleys into Macedonia.[99]
From Akanthos the fleet made its way by the canal through Athos to Therma, touching at various small Greek towns on the coast of the Chalkidike peninsula, and impressing ships and men from them.
The main army made its way direct across the base of the peninsula to Therma.
There the expedition rested.
From there the king went by ship to explore the great pass into Thessaly, where the river Peneius has cut the deep vale of Tempe between the heights of Olympus and Ossa. H. vii. 130. Herodotus takes the opportunity to put into his mouth some striking comments on the physical peculiarities of the region, which are, no doubt, the historian’s own, derived from the personal knowledge of the land.
From Tempe Xerxes returned to the army at Therma.
It was after Xerxes had reached Therma that the real difficulties of his land march began. Hitherto the route had traversed that north shore of the Ægean along which, between the mountains and the sea, nature has provided a strip of lowland which, though narrow, does not present great physical obstacles to the march of an army. But now all was different. It was as though, after traversing an unimpeded high road, he had to enter upon a region of enclosures, whose mountain walls, stupendous in difficulty, if not in height, forced him to take a winding pathway leading from one to the other of the narrow passages by which these walls were pierced. But this was not the only serious consideration which those in charge of the expedition had to face.
Hitherto the line of march, which had lain along the immediate sea coast, had been peculiarly favourable to the plan of advance adopted,—a plan founded essentially on the co-operation of the fleet with the land forces.
It may well be supposed that the dual nature of this advance was largely designed with intent to supply the commissariat of the army, as well as with the idea of military co-operation between it and the fleet.