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.