The methods of early agriculture might be dismissed as being mainly of archaeological interest, were it not for the advanced techniques that were developed in the great river valleys to feed water to the crops. It is possible that man as a food-gatherer early learned to encourage the growth of wild plants by splashing water on to the banks of a spring or stream; it is certain that the shaduf, still widely used, was being employed to water the date palms and vines, the vegetable plots and flower beds of the Egyptians in the second millennium B.C.

The shaduf is usually made by erecting two pillars, some 5 ft or more high, joined near the top by a short beam. Over this a long pole is balanced, which has at one end a vessel to hold water and at the other a counterpoise. A man standing at the water's edge fills the receptacle by dipping, raises it, and empties it into an irrigation channel. With this device a man can raise about 600 gallons to a height of 6 ft in a day. Rather later, shadufs were arranged in series, of which all except the first dipped into a trough filled by the preceding shaduf. Their first serious rival was perhaps a continuous chain of buckets--such as was apparently used to raise water from a well beneath the famous Hanging Gardens of Babylon. The ox-driven water-wheel, which can irrigate half an acre a day, is not known to have been in existence before c. 200 B.C., when the use of gearing to link a vertical shaft to that of a horizontal wheel became established.

Men must have dug for water in early times as the bedouin still dig in Arabia, deepening a hole in a likely place until either the water is found or patience is exhausted. For a permanent water-hole there  would be a lining of rough stone or other hard material and probably a rope and tackle erected over the mouth of the well, so that the water could be drawn by a downward haul. Since 1500 B.C. at latest, such tackle--and the shaduf--has often been equipped with a simple pulley. Wells in the wadis were not usually more than 15 ft deep; in cities they often went deeper, and at Nimrud excavation of the Assyrian palace of the ninth century B.C. has revealed a well, still holding water, more than 300 brick courses deep. But it seems likely that deep wells were first dug by percussion drilling when the ancient Egyptians, in their efforts to exploit the desert oases, discovered the possibility of making an artesian well; that is, one in which the water is forced upwards from a deep bore-hole by its own pressure.

The conservation of water by damming occasioned some of the earliest of the surviving large-scale works of man. The Orontes valley in Syria has a stone dyke 1 1/4 miles long, dating from about the year 1300 B.C.; an Assyrian dam above Nineveh still stands in part at a height of nearly 10 feet. There are also innumerable remains of cement-lined tanks and stone cisterns used for storing water, including cisterns hollowed underground in the rock to diminish evaporation, not to mention traces of vast engineering structures, such as aqueducts and underground conduits of stone or baked clay, which brought water to the cities, often from considerable distances.

In Egypt and Mesopotamia alike the main problem of settlement in the great valleys was irrigation. The annual rise of the Nile between July and September is an event at once so punctual and of such paramount importance that the making of the relevant calculations as to date and height were two technical functions which largely gave the priesthood its power. Menes, the legendary first pharaoh, is supposed to have dammed the Nile; history, however, cannot identify the moment at which man first attempted to retain the life-giving waters with a barrier of stone and mud. The system that evolved was the division of the cultivable area of the valley into rectangular basins of between 1,000 and 40,000 acres apiece, which were fed with water from the annual inundation by a system of sluices. Each of them in turn was flooded to a depth of from 3 to 6 ft, the water being held for a month or more to saturate the soil, after which the surplus was drained off to a lower level and returned eventually to the Nile. Areas to which the flood water would not flow naturally were fed by a system of canals.

The Tigris and Euphrates presented a different problem from the Nile, requiring a different solution. Their flooding is both dangerous and irregular; the Tigris rises before the Euphrates, which carries twice as much water and recedes more rapidly; and between them they carry five times as much sediment as the Nile, which choked the canals. Moreover, the flood ends at the beginning of the hot season, so that it is not enough to soak the ground thoroughly once, as in the Nile valley. Agriculture depended therefore upon a system of constant irrigation.

The lower valleys of the Tigris and the Euphrates were intersected by a series of large canals, the most famous of which, the Nahrwan, was 400 ft wide and probably more than 200 miles long. From them the water passed through feeder-canals into a network of smaller water channels and irrigation ditches, and from these last a trickle of water would be run into a single plot at a time. To maintain a flow through the system the main canal must have had its water-level a little above the general level of the land, and its flow must have been so regulated that it would neither wear away the banks through excessive speed nor become choked with silt and weeds as a result of sluggishness. At their heads, the canals depended upon great brick-built barrages and river weirs. Besides the use of brick and of reed-matting to strengthen banks of alluvial mud, the main requirement for constructing this vast irrigation system was a mass of workers equipped with picks and shovels. The countryside therefore flourished when a strong ruler like Hammurabi could compel each district to carry out its due share of such work, as his letters show he did, and the laws enforced a meticulous respect for the irrigation rights on which the value of the closely-defined landed property depended: Herodotus reports that, though it might sound incredible, the Babylonian farmer commonly obtained a yield of 200- and sometimes 300-fold on his corn. But a water system so elaborate and so rewarding was also extremely vulnerable: it is said that the Land of the Two Rivers has not yet recovered from the disrepair into which the canals fell during the Mongol invasions of the thirteenth and fourteenth centuries A.D. . .

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