Besides this, the condition of the estuary seemed to prohibit all attack
from that side. The space between Bît-Yakîn and the long line of dunes
or mud-banks which blocked the entrance to it was not so much a gulf as
a lagoon of uncertain and shifting extent; the water flowed only in
the middle, being stagnant near the shores; the whole expanse was
irregularly dotted over with mud-banks, and its service was constantly
altered by the alluvial soil brought down by the Tigris, the Euphrates,
the Ulaî, and the Uknu. The navigation of this lagoon was dangerous,
for the relative positions of the channels and shallows were constantly
shifting, and vessels of deep draught often ran aground in passing from
one end of it to the other.*

* The condition I describe here is very similar to what
Alexander's admirals found 350 years later. Arrian has
preserved for us the account of Nearchus' navigation in
these waters, and his description shows such a well-defined
condition of the estuary that its main outline must have
remained unchanged for a considerable time; the only
subsequent alterations which had taken place must have been
in the internal configuration, where the deposit of alluvium
must have necessarily reduced the area of the lake since the
time of Sennacherib. The little map on the next page has no
pretension to scientific exactitude; its only object is to
show roughly what the estuary of the Euphrates was like, and
to illustrate approximately the course of the Assyrian
expedition.

[Illustration: 048.jpg MAP THE NAR-MARRATUM IN THE TIME OF SENNACHERIB]

Sennacherib decided to march his force to the mouth of the Euphrates,