So much is readily intelligible.

But what at this time withheld Sapor, when he had so grand an opportunity of making an impression upon Rome--what paralyzed his arm when it might have struck with such effect it is far from easy to understand, though perhaps not impossible to conjecture.

The historian of the war ascribes his abstinence to a religious motive, telling us that the auguries were not favorable for the Persians crossing the Tigris.

But there is no other evidence that the Persians of this period were the slaves of any such superstition as that noted by Ammianus, nor any probability that a monarch of Sapor's force of character would have suffered his military policy to be affected by omens.

We must therefore ascribe the conduct of the Persian king to some cause not recorded by the historian--same failure of health, or some peril from internal or external enemies which called him away from the scene of his recent exploits, just at the time when his continued presence there was most important.