Amida, now Diarbekr, was situated on the right bank of the Upper Tigris, in a fertile plain, and was washed along the whole of its western side by a semi-circular bend of the river. It had been a place of considerable importance from a very ancient date, and had recently been much strengthened by Constantius, who had made it an arsenal for military engines, and had repaired its towers and walls. The town contained within it a copious fountain of water, which was liable, however, to acquire a disagreeable odor in the summer time. Seven legions, of the moderate strength to which legions had been reduced by Constantine, defended it; and the garrison included also a body of horse-archers, composed chiefly or entirely of noble foreigners. Sapor hoped in the first instance to terrify it into submission by his mere appearance, and boldly rode up to the gates with a small body of his followers, expecting that they would be opened to him. But the defenders were more courageous than he had imagined. They received him with a shower of darts and arrows that were directed specially against his person, which was conspicuous from its ornaments; and they aimed their weapons so well that one of them passed through a portion of his dress and was nearly wounding him. Persuaded by his followers, Sapor upon this withdrew, and committed the further prosecution of the attack to Grumbates, the king of the Chionites, who assaulted the walls on the next day with a body of picked troops, but was repulsed with great loss, his only son, a youth of great promise, being killed at his side by a dart from a balista. The death of this prince spread dismay through the camp, and was followed by a general mourning; but it now became a point of honor to take the town which had so injured one of the great king's royal allies; and Grumbates was promised that Amida should become the funeral pile of his lost darling.
The town was now regularly invested. Each nation was assigned its place. The Chionites, burning with the desire to avenge their late defeat, were on the east; the Vertse on the south; the Albanians, warriors from the Caspian region, on the north; the Segestans, who were reckoned the bravest soldiers of all, and who brought into the field a large body of elephants, held the west. A continuous line of Persians, five ranks deep, surrounded the entire city, and supported the auxiliary detachments. The entire besieging army was estimated at a hundred thousand men; the besieged, including the unarmed multitude, were under 30,000. After the pause of an entire day, the first general attack was made. Grumbates gave the signal for the assault by hurling a bloody spear into the space before the walls, after the fashion of a Roman fetialis. A cloud of darts and arrows from every side followed the flight of this weapon, and did severe damage to the besieged, who were at the same time galled with discharges from Roman military engines, taken by the Persians in some capture of Singara, and now employed against their former owners. Still a vigorous resistance continued to be made, and the besiegers, in their exposed positions, suffered even more than the garrison; so that after two days the attempt to carry the city by general assault was abandoned, and the slow process of a regular siege was adopted. Trenches were opened at the usual distance from the walls, along which the troops advanced under the cover of hurdles towards the ditch, which they proceeded to fill up in places. Mounds were then thrown up against the walls; and movable towers were constructed and brought into play, guarded externally with iron, and each mounting a balista. It was impossible long to withstand these various weapons of attack. The hopes of the besieged lay, primarily, in their receiving relief from without by the advance of an army capable of engaging their assailants and harassing them or driving them off; secondarily, in successful sallies, by means of which they might destroy the enemy's works and induce him to retire from before the place.