There were canals innumerable, and always the wind and the windmills. It is curious that he traces the Helmund as running to Seistan first and then to the Darya-i-Zarah. This is in fact correct, only the Darya-i-Zarah (or Gaod-i-Zireh, as we know it) receives no water from the Helmund until the great Hamún (lagoons) to the north of Nasratabad are filled to overflow. He also mentions two rivers as flowing into the Zarah--one from Farah (an important place in his time), which is impossible, as it would have to cross the Helmund; and one from Ghur. This indicates almost certainly that the name Zarah was not confined, as it is now, to the great salt swamp south of Rudbar on the Helmund, but it included the Hamúns north of Nasratabad, into which the Farah River and the Ghur River do actually empty themselves. At present these two great lake systems are separated by about 120 miles of Helmund River basin, and are only connected occasionally in flood time by means of the overflow (called Shelag) already referred to. The mention of Bist, and of the bridge of boats across the river at that point, is important, for it is clear that about the year A.D. 950 one high-road for trade eastward was across the desert, _i.e._ _via_ the Khash Rud valley from Zarinje to about the meridian of 63 E.L. and then straight over the desert to Bist (Kala Bist of modern mapping). The further mention of robats (or resting-places) _en route_, indicates that it was well kept up and a much traversed high-road. Subsequently Girishk appears to have become the popular crossing-place of the river, but it is well to remember that the earlier route still exists, and could readily be made available for a flank march on Kandahar. From Idrisi's writings we learn that a century later, _i.e._ about the end of the eleventh century, the Seistan province extended far beyond its present limits. Bamian and Ghur (_i.e._ the central hills of Afghanistan) were _vis-à-vis_ to that province; Farah was included; and probably the whole line of the frontier hills from the Sulimanis, opposite Multan, to Sibi and Kalat. It was an enormous province, and a new light breaks on its traditional wealth in grain and agricultural produce when we understand its vast extent.