Geography and geology
Nubia is quintessentially the land of the famous Nile Cataracts (First, Second, Third, Fourth, Fifth, and Sixth). These granite outcrops formed a sufficient impediment to travel to deter the expansion of the Egyptians, leaving the land in the possession of its indigenous Nubian population. The cataracts are at the same time symptomatic of the rugged terrain in much of the country, with its limited agrarian resources -- another reason why the land did not attract Egyptian settlers.
Nubia, no less than Egypt, is "the gift of the Nile," which is the source of nearly all life and livelihood. Beyond its floodplain, through most of the region, there is nothing but lifeless desert. Nowhere, however, is there the broad and rich floodplain which is the heart and soul of Egypt. The river is bordered by the same rich black soils as in Egypt, but here they occur only in discontinuous patches interrupted by areas where the river is directly bordered by cliffs or dunes. Moreover, through most of Nubia, the Nile does not regularly overflow its high banks during the flood season, and water for irrigation must always be raised by artificial means. The patches of alluvium, wherever they occur, are intensively cultivated, but they cannot support anything like the huge peasant population of Egypt. Except in its most southerly part, therefore, Nubia may be described as a country 1000 km long and 1 km wide.
The major cataracts, which are on the average about 150 to 200 km apart, serve to divide Nubia into a succession of quite distinct regions. The most northerly region, between the First and Second Cataracts, is traditionally called Lower Nubia. Here the river flows between low sandstone bluffs, sometimes right beside the river, and sometimes up to half a kilometer back. Alluvium, though not continuous, was more abundant here than in most of the rest of the country, and Lower Nubia always supported some of Nubia's most important and richest settlements. Commerce was enhanced by the fact that between the First and Second Cataracts there were no lesser rapids, making boat travel easy and safe. This region was the heartland of the medieval Kingdom of Nobadia. Today, however, its entire length lies beneath the waters of Lake Nasser, impounded by the Aswan High Dam.
Much of the region between the Second and Third Cataracts is a land where the sandstone overlay has been eroded away and the underlying "basement complex" of granite is exposed at the surface, resulting in a topography of rugged crags and ridges that occasionally approach the dimensions of true mountains. The northern half of this region is in fact known in Arabic as the Batn el-Hajjar - the "belly of rocks." The course of the river is impeded every few kilometers by rapids, each of which is a major deterrent to navigation. Alluvial deposits are especially scarce, and this region was always the least productive and least populated part of Nubia. It lay in medieval times within the Kingdom of Nobadia, but was of little economic or political importance until it became a place of refuge during the disturbed conditions of Late Christian times.
The land between the Third and Fourth Cataracts is by contrast the most fertile part of Nubia. It is again a sandstone region geologically and topographically similar to Lower Nubia, but it has in addition two fairly sizable basins where the river regularly overflows its banks during the flood season, making possible the kind of basin irrigation practiced throughout most of Egypt. This region was always, and remains today, the most populous part of Nubia. In medieval times it was the heartland of the Kingdom of Makouria, and before that of the Empire of Kush, at least in its earlier years. The capital cities of both Makouria and Kush were located here.
The region between the Fourth and Fifth Cataracts is again a region of granite outcrops, numerous rapids, and little alluvium. It belonged to the Kingdom of Makouria, but had fewer important settlements than any other part of Nubia.
South of the Fifth Cataract there is once again a more open and productive region, with no more rapids except for the relatively minor granite irruption of the Sixth Cataract. This region belonged to the medieval Kingdom of Alodia. It is populous and prosperous today, and probably was also in medieval times, but it has been so little explored archaeologically that nothing is really known about the conditions of earlier times.
Only in the most southerly part of Nubia is there sufficient rainfall to support seasonal stands of grass in the hinterland of the Nile Valley. As a result, dwellers in the southern region have always had to content with pastoral nomad neighbors, who were often a threat to the settled farmers. They were rarely if ever brought under the control over the riverain kingdoms.
Rainfall is scant throughout the whole of Nubia, varying from less than 10 mm anually at the north of the region to about 50 mm at its southern extremity. All agriculture therefore depends on irrigation from the Nile. There is no other water source except in the far south, where the tributary Atbara River has a seasonal flow.
Sources: Trigger 1965, 10-34; Adams 1977, 13-43.
(Contributed by William Y. Adams.)