While a part of the army (30,000 men, according to Ammianus Marcellinus) was dispatched north-east under his cousin Procopius and Count Sebastian to enlist the aid of Arshak II of Armenia for a march down the Tigris to Ctesiphon; Julian himself, with a larger force (65,000), penetrated Assyria to the south, proceeding along the Euphrates from Callinicum with the same ultimate destination.
However, these obstacles were surmounted; Anah capitulated; Macepracta was subdued; Pirisabora was reduced and sacked, and Julian promptly arrived under the walls of Maiozamalcha, a strongly fortified place 11 miles from the Persian capital of Ctesiphon.
A train of catapults and siege engines had attended the emperor's march through Assyria, and Julian employed them in vain against the impregnable fortifications; the frontal assault turned out to be a distraction from his real device.
While the assault on the walls was repelled by a vigorous Persian defense, a mine was surreptitiously built under the very feet of defenders thanks to Julian's engineers, by means of which three cohorts, or 1,500 of the elite of the Roman soldiers, crept into the heart of the city.
The city was instantly captured from the inside out with no mercy shown towards the astonished defenders or populace, who before its fall had - in insolent assurance - insulted Julian's arms and ally, the renegade prince of the Persian royal house, Hormisdas (or Hormizd).