The army moved on by a slow and toilsome progress until it reached the neck of the peninsula, and then turning at the head of the bay, it moved westward again, following the direction of the coast. The line of march was, however, laid at some distance from the shore, partly for the sake of avoiding the indentations made in the land by gulfs and bays, and partly for the sake of crossing the streams from the interior at points so far inland that the water found in them should be fresh and pure. Notwithstanding these precautions, however, the water often failed. So immense were the multitudes of men and of beasts, and so craving was the thirst which the heat and the fatigues of the march engendered, that, in several instances, they drank the little rivers dry.
The first great and important river which the army had to pass after entering Europe was the Hebrus. Not far from the mouth of the Hebrus, where it emptied into the Ægean Sea, was a great plain, which was called the plain of Doriscus. There was an extensive fortress here, which had been erected by the orders of Darius when he had subjugated this part of the country. The position of this fortress was an important one, because it commanded the whole region watered by the Hebrus, which was a very fruitful and populous district. Xerxes had been intending to have a grand review and enumeration of his forces on entering the European territories, and he judged Doriscus to be a very suitable place for his purpose. He could establish his own head-quarters in the fortress, while his armies could be marshaled and reviewed on the plain. The fleet, too, had been ordered to draw up to the shore at the same spot, and when the army reached the ground, they found the vessels already in the offing.
The army accordingly halted, and the necessary arrangements were made for the review. The first thing was to ascertain the numbers of the troops; and as the soldiers were too numerous to be counted, Xerxes determined to _measure_ the mighty mass as so much bulk, and then ascertain the numbers by a computation. They made the measure itself in the following manner: They counted off, first, ten thousand men, and brought them together in a compact circular mass, in the middle of the plain, and then marked a line upon the ground inclosing them. Upon this line, thus determined, they built a stone wall, about four feet high, with openings on opposite sides of it, by which men might enter and go out. When the wall was built, soldiers were sent into the inclosure--just as corn would be poured by a husbandman into a wooden peck--until it was full. The mass thus required to fill the inclosure was deemed and taken to be ten thousand men. This was the first filling of the measure. These men were then ordered to retire, and a fresh mass was introduced, and so on until the whole army was measured. The inclosure was filled one hundred and seventy times with the foot soldiers before the process was completed, indicating, as the total amount of the infantry of the army, a force of one million seven hundred thousand men. This enumeration, it must be remembered, included the land forces alone.