Cercasorus, near Heliopolis, where it bifurcated, was in general north,
with, however, a certain tendency westward. It entered Egypt nearly in
long. 33°, and at Neapolis (more than two degrees further north) it was
still within 15° of the same meridian; then, however, it took a westerly
bend, crossed the 32nd and 31st meridians, and in lat. 28° 23 reached
west as far as long. 30° 43'. After this it returned a little eastward,
recrossed the 31st meridian, and having reached long. 31° 22' near
Aphroditopolis (lat.29° 25), it proceeded almost due north to Cercasorus
in lat. 30° 7'. The course of the river up to this point was, from its
entry into the country, about 540 miles. At Cercasorus the Delta began.
The river threw out two branches, which flowed respectively to the
north-east and the north-west, while between them was a third channel,
a continuation of the previous course of the stream, which pierced the
Delta through its centre, flowing almost due north. Lower down, further
branch channels were thrown out, some natural, some artificial, and the
triangular tract between the two outer arms of the river was intersected
by at least five, and (in later times) by fourteen large streams. The
right and left arms appear to have been of about equal in length, and
may be estimated at 150 or 160 miles; the central arm had a shorter
course, not exceeding 110 miles. The volume of water which the Nile
pours into the Mediterranean during a day and night is estimated at from
150,000 millions to 700,000 millions of cubic metres. It was by far the
largest of all the rivers of the Empire.

The Indus, which was the next largest of the Persian rivers to the Nile,
rose (like the Nile) outside the Persian territory. Its source is in the
region north of the Himalaya range, about lat. 31°, long. 82° 30'. It
begins by flowing to the north-west, in a direction parallel to that of
the Western Himalayas, along the northern flank of which it continues
in this line a distance of about 700 miles, past Ladak, to long. 75°