Guran branch, which is known by the name of the Gamas-ab. The river
thus formed flows westward to Behistun, after which it bonds to the
south-west, and then to the south, receiving tributaries on both hands,
and winding among the mountains as far as the ruined city of Rudbar.
Here it bursts through the outer barrier of the great range, and,
receiving the large stream of the Kirrind from the north-west, flows
S.S.E. and S.E. along the foot of the range, between it and the Kebir
Kuh, till it meets the stream of the Abi-Zal, when it finally leaves the
hills and flows through the plain, pursuing a S.S.E. direction to the
ruins of Susa, which lie upon its left bank, and then turning to the
S. S. W., and running in that direction to the Shat-el-Arab, which it
reaches about five miles below Kurnur. Its length is estimated at above
500 miles; its width, at some distance above its junction with the
Abi-Zal, is from eighty to a hundred yards.

The course of the Kerkhah was not always exactly such as is here
described. Anciently it appears to have bifurcated at Pai Pul, 18 or 20
miles N.W. of Susa, and to have sent a branch east of the Susa ruins,
which absorbed the Shapur, a small tributary of the Dizful stream, and
ran into the Kuran a little above Ahwaz. The remains of the old channel
are still to be traced; and its existence explains the confusion,
observable in ancient times, between the Kerkhah and the Kuran, to each
of which streams, in certain parts of their course, we find the name
Eulseus applied. The proper Eulseus was the eastern branch of the
Kerkhah (Choaspes) from Pai Pul to Ahwaz; but the name was naturally
extended both northwards to the Choaspes above Pai Pul and southwards to
the Kuran below Ahwaz. The latter stream was, however, known also, both
in its upper and its lower course, as the Pasitigris.

On the opposite side of the Empire the rivers were less considerable.