It might have been expected that an advance would have at once been directed on Ctesiphon, the Parthian capital; but Trajan, for some reason which is not made clear to us, determined otherwise. He repassed the Tigris into Mesopotamia, took Hatra (now el-Hadhr), at that time one of the most considerable places in those parts, and then, crossing to the Euphrates, descended its course to Hit and Babylon. No resistance was offered him, and he became master of the mighty Babylon without a blow. Seleucia seems also to have submitted; and it remained only to attack and take the capital in order to have complete possession of the entire region watered by the two great rivers. For this purpose a fleet was again necessary, and, as the ships used on the upper Tigris had, it would seem, been abandoned, Trajan conveyed a flotilla, which had descended the Euphrates, across Mesopotamia on rollers, and launching it upon the Tigris, proceeded to the attack of the great metropolis. Here again the resistance that he encountered was trivial. Like Babylon and Seleucia, Ctesiphon at once opened its gates. The monarch had departed with his family and his chief treasures,6 and had placed a vast space between himself and his antagonist. He was prepared to contend with his Roman foe, not in battle array, but by means of distance, natural obstacles, and guerilla warfare. He had evidently determined neither to risk a battle nor stand a siege. As Trajan advanced, he retreated, seeming to yield all, but no doubt intending, if it should be necessary, to turn to bay at last, and in the meantime diligently fomenting that spirit of discontent and disaffection which was shortly to render the further advance of the Imperial troops impossible.