The latter now known as the Girduni Sudurrah pass, constitutes the famous "Pylae Caspiae." Through this pass alone can armies proceed from Armenia, Media, and Persia eastward, or from Turkestan, Khorasan, and Afghanistan into the more western parts of Asia.

The position is therefore one of primary importance.

It was to guard it that Rhages was built so near the eastern end of its territory.

So long as it remained in the possession of Syria, Parthian aggression was checked.

Rhagiana, the rest of Media, and the other provinces were safe, or nearly so.