It happened that at the time there were some other outstanding disputes, which caused the relations of the two empires to be less amicable than was to be desired.  The Persians had recently begun to work their gold mines, and had hired experienced persons from the Romans, whose services they found so valuable that when the period of the hiring was expired they would not suffer the miners to quit Persia and return to their homes.  They are also said to have ill-used the Roman merchants who traded in the Persian territories, and to have actually robbed them of their merchandise.

These causes of complaint were not, however, it would seem, brought forward by the Romans, who contented themselves with simply refusing the demand for the extradition of the Christian fugitives, and refrained from making any counter-claims.  But their moderation was not appreciated; and the Persian monarch, on learning that Rome would not restore the refugees, declared the peace to be at an end, and immediately made preparations for war.  The Romans had, however, anticipated his decision, and took the field in force before the Persians were ready.  The command was entrusted to a general bearing the strange name of Ardaburius, who marched his troops through Armenia into the fertile province of Arzanene, and there defeated Narses, the leader whom Varahran had sent against him.  Proceeding to plunder Arzanene, Ardaburius suddenly heard that his adversary was about to enter the Roman province of Mesopotamia, which was denuded of troops, and seemed to invite attack.  Hastily concluding his raid, he passed from Arzanene into the threatened district, and was in time to prevent the invasion intended by Narses, who, when he found his designs forestalled, threw himself into the fortress of Nisibis, and there stood on the defensive.  Ardaburius did not feel himself strong enough to invest the town; and for some time the two adversaries remained inactive, each watching the other.  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.