Herodotus tells us distinctly what _he_ meant by a parasang, and what the Persian government of his day recognized as such in their measurement of the great road from Sardis to Susa, as well as in their measurements of territory for purposes of tribute (Herod. v, 53; vi, 43). It was thirty Greek stadia = nearly three and a half English miles, or nearly three geographical miles. The distance between every two successive stations, on the road from Sardis to Susa, (which was “all inhabited and all secure,” διὰ οἰκεομένης τε ἅπασα καὶ ἀσφολέος), would seem to have been measured and marked in parasangs and fractions of a parasang. It seems probable, from the account which Herodotus gives of the march of Xerxes (vii, 26), that this road passed from Kappadokia and across the river Halys, through Kelænæ and Kolossæ to Sardis; and therefore that the road which Cyrus took for his march, from Sardis at least as far as Kelænæ, must have been so measured and marked. Xenophon also in his summing up of the route, (ii, 2, 6; vii, 8, 26) implies the parasang as equivalent to thirty stadia, while he gives for the most part, each day’s journey measured in parasangs. Now even at the outset of the march, we have no reason to believe that there was any official measurer of road-progress accompanying the army, like Bæton, ὁ Βηματιστὴς Ἀλεξάνδρου, in Alexander’s invasion; see Athenæus, x, p. 442, and Geier, Alexandri Magni Histor. Scriptt. p. 357. Yet Xenophon, throughout the whole march, even as far as Trebizond, states the day’s march of the army in parasangs; not merely in Asia Minor, where there were roads, but through the Arabian desert between Thapsakus and Pylæ,—through the snows of Armenia,—and through the territory of the barbarous Chalybes. He tells us that in the desert of Arabia they marched ninety parasangs in thirteen days, or very nearly seven parasangs per day,—and that too under the extreme heat of summer. He tells us, farther, that in the deep snows of Armenia, and in the extremity of winter, they marched fifteen parasangs in three days; and through the territory (also covered with snow) of the pugnacious Chalybes, fifty parasangs in seven days, or more than seven parasangs per day. Such marches, at thirty stadia for the parasang, are impossible. And how did Xenophon measure the distance marched over?