cupation. 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.

The Persians now for the first time appeared in force. As Julian drew
near the great stream, he perceived that his passage of it would not be
unopposed. Along the left bank, which was at this point naturally higher
than the right, and which was further crowned by a wall b