The river Mygdonius (now the Jerujer), swollen by the melting of the snows in the Mons Masius, had overflowed its banks and covered with an inundation the plain in which Nisibis stands.

Sapor saw that the forces of nature might be employed to advance his ends, and so embanked the lower part of the plain that the water could not run off, but formed a deep lake round the town, gradually creeping up the walls till it had almost reached the battlements.

Having thus created an artificial sea, the energetic monarch rapidly collected, or constructed, a fleet of vessels, and, placing his military engines on board, launched the ships upon the waters, and so attacked the walls of the city at great advantage.

But the defenders resisted stoutly, setting the engines on fire with torches, and either lifting the ships from the water by means of cranes, or else shattering them with the huge stones which they could discharge from their balistics.

Still, therefore, no impression was made; but at last an unforeseen circumstance brought the besieged into the greatest peril, and almost gave Nisibis into the enemy's hands.