Mary Shelley refers to the account of the long Greek retreat from Armenia in Xenophon's
                     Anabasis, 4.7, quoted here in the translation of Carleton L. Brownson (Cambridge:
                     Harvard University Press, 1918): 
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 [18] Leaving this land [of the Chalybians], the Greeks arrived at the Harpasus river,
                     which was four plethra in width. From there they marched through the territory of
                     the Scythinians four stages, twenty parasangs, over a level plain, and they arrived
                     at some villages, and there remained for three days and collected provisions.
[19] From there they journeyed four stages, twenty parasangs, to a large and prosperous
                     inhabited city which was called Gymnias. From this city the ruler of the land sent
                     the Greeks a guide, in order to lead them through territory that was hostile to his
                     own. 
[20] When the guide came, he said that he would lead them within five days to a place
                     from which they could see the sea; if he failed to do so, he was ready to accept death.
                     Thus taking the lead, as soon as he had brought them into the hostile territory, he
                     kept urging them to spread abroad fire and ruin, thereby making it clear that it {331}
                     was with this end in view that he had come, and not out of good-will toward the Greeks.
                     
[21] On the fifth day they did in fact reach the mountain; its name was Theches. Now
                     as soon as the vanguard got to the top of the mountain, a great shout went up. 
[22] And when Xenophon and the rearguard heard it, they imagined that other enemies
                     were attacking in front; for enemies were following behind them from the district
                     that was in flames, and the rearguard had killed some of them and captured others
                     by setting an ambush, and had also taken about twenty wicker shields covered with
                     raw, shaggy ox-hides. 
[23] But as the shout kept getting louder and nearer, as the successive ranks that
                     came up all began to run at full speed toward the ranks ahead that were one after
                     another joining in the shout, and as the shout kept growing far louder as the number
                     of men grew steadily greater, it became quite clear to Xenophon that here was something
                     of unusual importance; 
[24] so he mounted a horse, took with him Lycius and the cavalry, and pushed ahead
                     to lend aid; and in a moment they heard the soldiers shouting, "The Sea! The Sea!"
                     and passing the word along. Then all the troops of the rearguard likewise broke into
                     a run, and the pack animals began racing ahead and the horses. 
[25] And when all had reached the summit, then indeed they fell to embracing one another,
                     and generals and captains as well, with tears in their eyes. And on a sudden, at the
                     bidding of some one or other, the soldiers began to bring stones and to build a great
                     cairn. 
[26] Thereon they placed as offerings a quantity of raw ox-hides and walking-sticks
                     and the captured wicker shields; and the guide not only cut these {333} shields to
                     pieces himself, but urged the others to do so. 
[27] After this the Greeks dismissed the guide with gifts from the common stock --
                     a horse, a silver cup, a Persian dress, and ten darics; but what he particularly asked
                     the men for was their rings, and he got a considerable number of them. Then he showed
                     them a village to encamp in and the road they were to follow to the country of the
                     Macronians, and, as soon as evening came, took his departure. 
(text from the Perseus Project, Tufts University)