Arsaces had expected Antiochus to advance as far as this region, but he did not think he would venture with such a large force to cross the adjacent desert, chiefly owing to the scarcity of water.
For in the region I speak of there is no water visible on the surface, but even in the desert there are a number of underground channels communicating with wells unknown to those not acquainted with the country.
About these a true story is told by the inhabitants. They say that at the time when the Persians were the rulers of Asia they gave to those who conveyed a supply of water to places previously unirrigated the right of cultivating the land for five generations,
and consequently as the Taurus has many large streams descending from it, people incurred great expense and trouble in making underground channels reaching a long distance, so that at the present day those who make use of the water do not know whence the channels derive their supply.
Arsaces, however, when he saw that Antiochus was attempting to march across the desert, endeavoured instantly to fill up and destroy the wells.
The king when this news reached him sent off Nicomedes with a thousand horse, who, finding that Arsaces had retired with his army, but that some of his cavalry were engaged in destroying the mouths of the channels, attacked and routed these, forcing them to fly, and then returned to Antiochus.
The king having traversed the desert came to the city called Hecatompylus, which lies in the centre of Parthia. This city derives its name from the fact that it is the meeting-place of all the roads leading to the surrounding districts.
Walbank Commentary