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.