Desertion and treachery were arrayed against them.

One of the natives of Amida, going over to the Persians, informed them that on the southern side of the city a neglected staircase led up from the margin of the Tigris through underground corridors to one of the principal bastions; and under his guidance seventy archers of the Persian guard, picked men, ascended the dark passage at dead of night, occupied the tower, and when morning broke displayed from it a scarlet flag, as a sign to their countrymen that a portion of the wall was taken.

The Persians were upon the alert, and an instant assault was made.

But the garrison, by extraordinary efforts, succeeded in recapturing the tower before any support reached its occupants; and then, directing their artillery and missiles against the assailing columns, inflicted on them tremendous losses, and soon compelled them to return hastily to the shelter of their camp.

The Verte, who maintained the siege on the south side of the city, were the chief sufferers in this abortive attempt.
Sapor had now spent seventy days before the place, and had made no perceptible impression.