Certainly between the present condition of things and that in the time of Alexander, or even of Herodotus, no great difference can be pointed out, except in the region immediately adjoining on the gulf, where the alluvium has grown, and the streams, which were formerly separate, have united their waters.

The Euphrates still flows by Hit and through Babylon; the Tigris passes near Opis, and at Baghdad runs at the foot of an embankment made to confine it by Nebuchadnezzar.
The changes traceable are less in the main courses than in the branch streams, which perpetually vary, being sometimes left dry within a few years of the time that they have been navigable channels.
The most important variations of this kind are on the side of Arabia.
Here the desert is always ready to encroach; and the limits of Chaldaea itself depend upon the distance from the main river, to which some branch stream conveys the Euphrates water.

In the most flourishing times of the country, a wide and deep channel, branching off near Hit, at the very commencement of the alluvium, has skirted the Arabian rock and gravel for a distance of several hundred miles, and has entered the Persian Gulf by a mouth of its own.

In this way the extent of Chaldaea has been at times largely increased, a vast tract being rendered cultivable, which is otherwise either swamp or desert.
Such are the chief points of interest connected with the two great Mesopotamian rivers.

These form, as has been already observed, the only marked and striking characteristics of the country, which, except for them, and for one further feature, which now requires notice, would be absolutely unvaried and uniform.