Though he still continued the siege for a while, he made no other grand attack, and at length drew off his forces, having lost twenty thousand men before the walls, and wasted a hundred days, or more than three months.
Perhaps he would not have departed so soon, but would have turned the siege into a blockade, and endeavored to starve the garrison into submission, had not alarming tidings reached him from his north-eastern frontier.

Then, as now, the low flat sandy region east of the Caspian was in the possession of nomadic hordes, whose whole life was spent in war and plunder.

The Oxus might be nominally the boundary of the empire in this quarter; but the nomads were really dominant over the entire desert to the foot of the Hyrcanian and Parthian hills.

Petty plundering forays into the fertile region south and east of the desert were no doubt constant, and were not greatly regarded; but from time to time some tribe or chieftain bolder than the rest made a deeper inroad and a more sustained attack than usual, spreading consternation around, and terrifying the court for its safety.

Such an attack seems to have occurred towards the autumn of A.D.350.