One of the sons of Sapor was now at their head, but no change of tactics occurred. As Julian drew near, this prince indeed quitted the shelter of Ctesiphon, and made a reconnaissance in force; but when he fell in with the Roman advanced guard under Victor, and saw its strength, he declined an engagement, and retired without coming to blows. Julian had now reached the western suburb of Ctesiphon, which had lost its old name of Seleucia and was known as Coche. The capture of this place would, perhaps, not have been difficult; but, as the broad and deep stream of the Tigris flowed between it and the main town, little would have been gained by the occupation. Julian felt that, to attack Ctesiphon with success, he must, like Trajan and Severus, transport his army to the left bank of the Tigris, and deliver his assault upon the defences that lay beyond that river. For the safe transport of his army he trusted to his fleet, which he had therefore caused to enter the Nahr-Malcha, and to accompany his troops thus far. But at Coche he found that the Nahr-Malcha, instead of joining the Tigris, as he had expected, above Ctesiphon, ran into it at some distance below. To have pursued this line with both fleet and army would have carried him too far into the enemy’s country, have endangered his communications, and especially have cut him off from the Armenian army under Procopius and Sebastian, with which he was at this time looking to effect a junction. To have sent the fleet into the Tigris below Coche, while the army occupied the right bank of the river above it, would, in the first place, have separated the two, and would further have been useless, unless the fleet could force its way against the strong current through the whole length of the hostile city. In this difficulty Julian’s book-knowledge was found of service. He had studied with care the campaigns of his predecessors in these regions, and recollected that one of them at any rate had made a cutting from the Nahr-Malcha, by which he had brought his fleet into the Tigris above Ctesiphon. If this work could be discovered, it might, he thought, in all probability be restored. Some of the country people were therefore seized, and, inquiry being made of them, the line of the canal was pointed out, and the place shown at which it had been derived from the Nahr-Malcha. Here the Persians had erected a strong dam, with sluices, by means of which a portion of the water could occasionally be turned into the Roman cutting. Julian had the cutting cleared out, and the dam torn down; whereupon the main portion of the stream rushed at once into the old channel, which rapidly filled, and was found to be navigable by the Roman vessels. The fleet was thus brought into the Tigris above Coche; and the army advancing with it encamped upon the right bank of the river.