Trajan about spring time proceeded into the enemy's country. Now since the region near the Tigris is barren of timbers fit for shipbuilding, he brought the boats which had been constructed in the forests surrounding Nisibis on wagons to the river. The vessels had been arranged in such a way that they could be taken apart and put together. He had very hard work in bridging the stream opposite Mount Carduenum, for the opposing barbarians tried to hinder him. Trajan, however, had a great abundance of both ships and soldiers, and so some boats were fastened together with great speed while others lay motionless in front of them, carrying heavy infantry and archers. Still others kept making dashes this way and that, as if they intended to cross. As a result of these tactics and from their very astonishment at seeing so many ships at once appear
en masse
from a land devoid of trees the barbarians gave way and the Romans crossed over. They won possession of the whole of Adiabene. (This is a portion of Assyria in the vicinity of Ninus; and Arbela and Gaugamela, close to which Alexander conquered Darius, are also in this same territory. The country has also been called Atyria in the language of the barbarians, the double S being changed to T).
[Adenystrae was a strong post to which one Sentius, a centurion, had been sent as an envoy to Mebarsapes. He was imprisoned by the latter in that place, and later, at the approach of the Romans, he made an arrangement with some of his fellow-prisoners, and with their aid escaped from his shackles, killed the commander of the garrison, and opened the gates to his countrymen.] Hereupon they advanced as far as Babylon itself, being quite free from molestation, since the Parthian power had been ruined by civil conflicts and was still at this time involved in dissensions.
27
Cassius Dio Cocceianus in writings concerning the Latins has written that this city [i.e. Babylon] comprised a circuit of four hundred stades. (Compare also Tzetzes, Exegesis of Homer's Iliad, p. 141, 15 ff).
Here, moreover, Trajan saw the asphalt out of which the walls of Babylon had been built. When mixed with baked bricks or smooth stones this material affords so great strength as to render them stronger than rock or any kind of iron. He also looked at the opening from which issues a deadly vapor that destroys any creature living upon the earth and any winged thing that so much as inhales a breath of it. If it extended far above ground or had several vents, the place would not be inhabitable; but, as it is, this gas circles round within itself and remains stationary. Hence creatures that fly high enough above it and such as remain to one side are safe. I saw another opening like it at Hierapolis in Asia, and tested it by means of birds; I bent over it myself and myself gazed down upon the vapor. It is enclosed in a sort of a cistern and a theatre had been built over it. It destroys all living things save human beings that have been emasculated. The reason for that I can not comprehend. I relate what I have seen as I have seen it and what I have heard as I have heard it.
A.D. 116 (a.u. 869)