by boats; the army marched on the natural ground along an established line of route which no art had prepared for the passage of man or beast.  Portions of the route would often be soft and muddy; the carts and litters would become immovable, their wheels sinking into the mire up to the axles; all the efforts of the teams would be unavailing; it must have been imperative to halt the main line, and employ the soldiers in the release of the vehicles, which had to be lifted and carried forward till the ground was sufficiently firm to bear them.  When a river crossed the line of route, a ford had to be sought, boats procured, or rafts extemporized.  The Persians were skilful in the passage of streams, to which they became accustomed in their first campaigns under Cyrus; but the march was necessarily retarded by these and similar obstacles, and we cannot be surprised that the average rate of movement was slow.

As evening approached the Persians sought a suitable place for their camp.  An open plain was preferred for the purpose, and the vicinity of water was a necessity.  If an enemy was thought to be at hand, a ditch was rapidly dug, and the earth thrown up inside; or if the soil was sandy, sacks were filled with it, and the camp was protected with sand-bags.  Immediately within the rampart were placed the gerrhophori, or Persians armed with large wicker shields.  The rest of the soldiers had severally their appointed places, the position assigned to the commander-in-chief being the centre.  All the army had tents, which were pitched so as to face the east.  The horses of the cavalry were tethered and hobbled in front of the tents of their owners.

The Persians disliked encamping near to their enemy.  They preferred an interval of seven or eight miles, which they regarded as a considerable security against a surprise.  As their most important arm was the cavalry, and as it was impossible for the cavalry to unfasten and unhobble their steeds, to equip them properly, to arm themselves, and then to mount in a short space of time, when darkness and confusion reigned around, a night attack on the part of an enterprising enemy would have been most perilous to a Persian army.  Hence the precaution which they observed against its occurrence—­a precaution which was seldom or never omitted where they felt any respect for their foe, and which seems to have been effective, since we do not hear of their suffering any disaster of the kind which they so greatly feared.

The Persians do not seem to have possessed any special corps of pioneers.  When the nature of the country was such as to require the felling of timber or the removal of brushwood, the army was halted, and the work was assigned to a certain number of the regular soldiers.  For the construction of bridges, however, in important places, and for other works on a grand scale intended to facilitate an expedition, preparations were made beforehand, the tasks being entrusted either to skilled workmen, or to the crews of ships, if they were tolerably easy of performance.