It was during this interval that (if we may credit Socrates) the Persian general sent a challenge to the Roman, inviting him to fix time and place for a trial of strength between the two armies.

Ardaburius prudently declined the overture, remarking that the Romans were not accustomed to fight battles when their enemies wished, but when it suited themselves.

Soon afterwards he found himself able to illustrate his meaning by his actions.

Having carefully abstained from attacking Nisibis while his strength seemed to him insufficient, he suddenly, upon receiving large reinforcements from Theodosius, changed his tactics, and, invading Persian Mesopotamia, marched upon the stronghold held by Narses, and formally commenced its siege.
Hitherto Varahran, confident in his troops or his good fortune, had left the entire conduct of the military operations to his general; but the danger of Nisibis--that dearly won and highly prized possession--seriously alarmed him, and made him resolve to take the field in person with all his forces.

Enlisting on his side the services of his friends the Arabs, under their great sheikh, Al-Amundarus (Moundsir), and collecting together a strong body of elephants, he advanced to the relief of the beleaguered town.