It occurred to the Emperor Justinian that the Persians would not, as far as lay in their power, permit this Roman fortress to stand threatening them, but that they would march against it with their entire force, and use every device to assault its walls on equal terms; and that a number of elephants would accompany them, bearing wooden towers upon their backs, which towers instead of foundations would rest upon the elephants, who—and this was the worst of all—could manœuvre round the city at the pleasure of the enemy, and carry a wall which could be moved whithersoever its masters might think fit; and the enemy, mounted upon these towers, would shoot down upon the heads of the Romans within the walls, and assail them from above; they would also pile up mounds of earth against the walls, and bring up to them all the machines used in sieges; while if any misfortune should befall the city of Dara, which was an outwork of the entire Roman Empire and a standing menace to the enemy’s country, the evil would not rest there, but the whole state would be endangered to a great extent. Moved by these considerations he determined to fortify the place in a manner worthy of its value. In the first place,[35] therefore, since the wall was, as I have described, very low, and therefore easily assailable, he rendered it inaccessible and altogether impregnable. He placed stones which so contracted the original battlements as only to leave small traces of them, like windows, allowing just so much opening to them as a hand could be passed through, so that passages were left through which arrows could be shot against the assailants. Above these he built a wall to a height of about thirty feet, not making the wall of the same thickness all the way to the top, lest the foundations should be over-weighted by the mass above, and the whole work be ruined; but he surrounded the upper part with a course of stones, and built a portico extending round the entire circuit of the walls, above which he placed the battlements, so that the wall was throughout constructed of two stories, and the towers of three stories, which could be manned by the defenders to repel the attacks of the enemy; for over the middle of the towers he constructed a vaulted roof, and again built new battlements above it, thus making them into a fortification consisting of three stories.