'IRAQ AND THE PERSIAN GULF' [‎279r] (560/862)

IRRIGATION, AGRICULTURE, AND MINOR INDUSTRY 433
were elaborated by the Achaemenid Persians (6th to 4th centuries
b.c.); canal construction from the Euphrates below Babylon was
undertaken by Alexander the Great (p. 33), and it is possible that
the Nahrwan system was at least begun in Seleucid times when
changes in the courses of the Tigris and Diyala may have occurred
(fig. 13; pp. 45-7).
The elaboration of the Nahrwan system and the development of
the waterways from the Euphrates to the Tigris below Falluja by the
Sassanid Persians (3rd to 7th century a.d.) and Abbasid Caliphs gave
to Mesopotamia what is to-day its greatest lack—a rudimentary
but sound system of land drainage which checked the formation of
stagnant water and the salination of the land. The two systems of
irrigation from the Nahrwan and Euphrates used the main bed of the
Tigris below Ctesiphon as a drain to collect the surplus water from
the land, a principle which formed the basis of these classical irriga
tion schemes.
The maximum development of the canal system was due to the
Abbasid Caliphs, who dug the Ishaqi-Dujail canals (fig. 74) on the
right bank of the Tigris, and built new head-works to the Nahrwan.
Large areas were brought under cultivation between Tikrit and
Samarra, and particularly on both sides of the Abbasid course of the
Tigris, by means of distributaries from the Dujail and the Nahrwan.
Control works were built on the Adhaim and Diyala to prevent
damage to the Nahrwan from winter spates. At the exit of the Adhaim
from the Jabal Hamrin a weir was constructed which prevented
excessive volumes of water in its lower reaches, and water was drawn
from the Little Zab to irrigate the plain north of the Jabal Hamrin
(p. 73). The Diyala was tapped for irrigation near its exit from the
hills, and its surplus waters controlled at various points as they
entered the Nahrwan. The districts north and east of Baghdad were
intensively irrigated by these canals, and a whole series of canals from
the Euphrates enriched the land between the two rivers south of the
capital (p. 31).
The common view that the ruin of the land was effected in a few
years by the destruction of irrigation head-works at the hands of
Mongol invaders in the thirteenth or fourteenth centuries a.d. is
certainly false. Some of the Euphrates canals were still in use in the
early nineteenth century when Chesney sailed down the Saqlawiya—
the Abbasid Nahr Isa (p. 30)—into the Tigris, but all had suffered
from administrative neglect and from the gradual silting up of both
main and branch canals over a period of centuries. It is relatively
A 5195 Ff