We know from Herodotus that all the territory of Babylonia was intersected by canals, and that there was one canal greater than the rest and navigable, which flowed from the Euphrates to the Tigris, in a direction to the south of east. This coincides pretty well with the direction assigned in Colonel Chesney’s map to the Nahr-Malcha or Regium Flumen, into which the four great canals, described by Xenophon as drawn from the Tigris to the Euphrates, might naturally discharge themselves, and still be said to fall into the Euphrates, of which the Nahr-Malcha was as it were a branch. How the level of the two rivers would adjust itself, when the space between them was covered with a network of canals great and small, and when a vast quantity of the water of both was exhausted in fertilizing the earth, is difficult to say. The _island_ wherein the Greeks stood, at their position near Sittakê, before crossing the Tigris, would be a parallelogram formed by the Tigris, the Nahr-Malcha, and the two parallel canals joining them. It might well be called a large island, containing many cities and villages, with a large population. After having crossed by a bridge laid upon thirty-seven pontoons, the Greeks continued their march to the northward upon the eastern side of the Tigris, for four days, to the river Physkus; said to be twenty parasangs.[122] The Physkus was one hundred feet wide, with a bridge, and the large city of Opis near it. Here, at the frontier of Assyria and Media, the road from the eastern regions to Babylon joined the road northerly on which the Greeks were marching. An illegitimate brother of Artaxerxes was seen at the head of a numerous force, which he was conducting from Susa and Ekbatana as a reinforcement to the royal army. This great host halted to see the Greeks pass by; and Klearchus ordered the march in column of two abreast, employing himself actively to maintain an excellent array, and halting more than once. The army thus occupied so long a time in passing by the Persian host, that their numbers appeared greater than the reality, even to themselves; while the effect upon the Persian spectators was very imposing.[123] Here Assyria ended and Media began. They marched, still in a northerly direction, for six days through a portion of Media almost unpeopled, until they came to some flourishing villages which formed a portion of the domain of queen Parysatis; probably these villages, forming so marked an exception to the desert character of the remaining march, were situated on the Lesser Zab, which flows into the Tigris, and which Xenophon must have crossed, though he makes no mention of it. According to the order of march stipulated between the Greeks and Tissaphernes, the latter only provided a supply of provisions for the former to purchase; but on the present halt, he allowed the Greeks to plunder the villages, which were rich and full of all sorts of subsistence,—yet without