Justinian sent 7,000 Roman and 1,000 Tzani (relatives of the Lazs) auxiliaries under Dagisthaeus to assist Gubazes, and besieged the Petra fortress, but faced a tough resistance from its heavilly outnumbered garrison. Persian reinforcements under Mihr-Mihroe defeated a small Byzantine force guarding the mountain passes and then relieved the besieged Petra. Mihr-Mihroe garrisoned 3,000 men in the fortress and marched to Armenia leaving 5,000 soldiers to plunder Lazica.