But Mermeroes, after passing the Iberian frontier with the whole Median army, was moving forward with the River Phasis on his right.  For he was quite unwilling to go through the country of Lazica, lest any obstacle should confront him there.  For he was eager to save the city of Petra and the Persians in it, even though a portion of the circuit-wall had fallen down suddenly.  For it had been hanging in the air, as I have said; and volunteers from the Roman army to the number of fifty got inside the city, and raised the shout proclaiming the Emperor Justinian triumphant.  These men were led by a young man of Armenian birth, John by name, the son of Thomas whom they used to call by the surname Gouzes.  This Thomas had built many of the strongholds about Lazica at the direction of the emperor, and he commanded the soldiers there, seeming to the emperor an intelligent person.  Now John, when the Persians joined battle with his men, was wounded and straightway withdrew to the camp with his followers, since no one else of the Roman army came to support him.  Meanwhile the Persian Mirranes who commanded the garrison in Petra, fearing for the city, directed all the Persians to keep guard with the greatest diligence, and he himself went to Dagisthaeus, and addressed him with fawning speeches and deceptive words, agreeing readily to surrender the city not long afterwards.  In this way he succeeded in deceiving him so that the Roman army did not immediately enter the city.

Now when the army of Mermeroes came to the pass, the Roman garrison, numbering one hundred men, confronted them there and offered a stalwart resistance, and they held in check their opponents who were attempting the entrance.  But the Persians by no means withdrew, but those who fell were constantly replaced by others, and they kept advancing, trying with all their strength to force their way in.  Among the Persians more than a thousand perished, but at last the Romans were worn out with killing, and, being forced back by the throng, they withdrew, and running up to the heights of the mountain there were saved.  Dagisthaeus, upon learning this, straightway abandoned the siege without giving any commands to the army, and proceeded to the River Phasis; and all the Romans followed him, leaving their possessions behind in the camp.  And when the Persians observed what was being done, they opened their gates and came forth, and approached the tents of the enemy in order to capture the camp.  But the Tzani, who had not followed after Dagisthaeus, as it happened, rushed out to defend the camp, and they routed the enemy without difficulty and killed many.  So the Persians fled inside their fortifications, and the Tzani, after plundering the Roman camp proceeded straight for Rhizaeum.  And from there they came to Athens and betook themselves to their homes through the territory of the Trapezuntines.