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 deg., long. 82 deg. 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 deg. nearly.  Here it is met by the Bolor chain, which prevents its further progress in this direction and causes it to turn suddenly nearly at a right angle to the south-west.  Entering a transverse valley, it finds a way (which is still very imperfectly known) through the numerous ridges of the Himalaya to the plain at its southern base, on which it debouches about thirty miles above Attock.  It is difficult to say at what exact point it crossed the Persian frontier, but probably at least the first 700 miles of its course were through territory not Persian.  From Attock to the sea the Indus is a noble river.  It runs for 900 miles in a general direction of S.S.W. through the plain in one main stream (which is several hundred yards in width), while on its way it throws off also from time to time small side streamlets, which are either consumed in irrigation or rejoin the main channel.  A little below Tatta its Delta begins—­a Delta, however, much inferior in size to that of the Nile.  The distance from the apex to the sea is not more than sixty miles, and the breadth of the tract embraced between the two arms does not exceed seventy miles.  The entire course of the Indus is reckoned at 1960 miles, of which probably 1260 were through Persian territory.  The volume of the stream is always considerable, while in the rainy season it is very great.  The Indus is said then to discharge into the Indian ocean 446,000 cubic feet per second, or 4280 millions of cubic yards in the twenty-four hours.