It is often good policy in such a case even to yield the capital without a blow, and to retreat into a more difficult situation.

The assailant must follow whithersoever his foe retires, or quit the country, leaving him unsubdued.

Antiochus, aware of this necessity, and rendered confident of success by the evacuation of a situation so strong, and so suitable for the Parthian tactics as Hecatompylos, after giving his army a short rest at the captured capital, set out in pursuit of Artabanus, who had withdrawn his forces towards Hyrcania.

To reach the rich Hyrcanian valleys, he was forced to cross the main chain of the Elburz, which here attains an elevation of 7000 or 8000 feet.

The route which his army had to follow was the channel of a winter-torrent, obstructed with stones and trunks of trees, partly by nature, partly by the efforts of the inhabitants.