Nisibis was won for Rome by the conquering arm of Lucullus. It was known then as Antioch in Mygdonia, because its fertile fields and shady groves irresistibly reminded the Graecian colonists of their lovely Antioch of Daphne. What a satire on Plutarch's explanation are the grim wastes which now environ it, and the barren hummocks of drift sand which have covered its ruins like a shroud! The Romans fortified the city with a triple rampart and a deep moat, and esteemed it (as it often proved itself) the principal bulwark of the east. They maintained a strong garrison in it; and the inhabitants, living in a state of constant warfare with the Parthians and Sassanid Persians, made almost as reliable soldiers as the regular legionaries themselves.
When Sapor II made war on Constantius it was Nisibis that checked his invasions. Between the years 338 and 350 it sustained no fewer than three sieges, and on each of those three occasions it repulsed the invader from its walls. The last siege was also the greatest. Sapor advanced to the attack at the head of an enormous army drawn from all parts of Persia and India, and pressed his assaults most vehemently for a period of over three months. The garrison was ably commanded by Count Lucilianus, but the soul of the defence was the celebrated bishop St. James of Nisibis; and Sapor, finding that he could make no impression by ordinary methods, conceived the idea of raising an enormous dam to obstruct the Jag-jag river (the ancient Mygdonius) and so flooding the place out. As the city lies in a slight depression this Gargantuan scheme was just feasible; and Sapor did actually contrive to create such an inundation that he could launch a fleet upon it and assail the defenders of the walls on level terms. The combined effect of the flood and the floating batteries opened a breach 150 feet wide, and the Great King ordered an immediate assault: but the attacking columns were bogged in the deep mud, and environed by invisible pot-holes; and to cap all, the elephants stampeded and trampled them underfoot by scores. At nightfall the Persians drew off, and the breach was repaired before morning. Sapor had lost 20,000 soldiers and broke up the siege in despair. Legend asserts that his retreat was much expedited by a prodigious plague of flies which descended on the Persian camp in response to the sainted bishop's orisons: but a sceptic might argue that when you have an Oriental army, with its usual disregard of every possible sanitary precaution, encamping in a marsh for three months during the height of a Mesopotamian summer, it needs no miraculous interference to account for something phenomenal in the way of flies!