High Dam is one of the most important achievements in the last century in Egypt; it is still the symbol of the New Era of the Revolution of 1952.

Back on the road south and 5 m from town you come to the old Aswan Dam, built by the British between 1898 and 1902. The road passes over it and across the first Cataract; the water swirls round the ragged stones, plays white, but has lost its boll.

The height of the dam was twice raised to increase irrigation and its hydroelectric capacity was multiplied, but Egypt's fast growing population and the need both to increase her cultivated land area and to provide vast new supplies of power for a necessary industrialsation programme, led to work beginning in the mid-1960 on the High Dam 6 km upriver.

The road linking the tow runs through distributed desert on the west bank, a giant disused sand pit it seems; you cannot imagine that this is the shore of uncharted Sand Ocean going on forever. Numerous electricity pylons add to the impression of it being a man made litter ground. At the west approach to the dam there is a giant lotus-shaped monument originally commemorating Soviet-Egyptian co-operation. The police here take the opportunity to check your papers and impose a change.

The High Dam has command world attention. Its construction became a political issue between East and West. Its sheer size, its effect on the economic potential of the country, and the sudden attention it forced on the Nubian antiquities threatened by the rising waters of lake Nasser. Have all been extraordinary.

The dam was completed in 1971 and since then the water contained by it has reached a height of 182m and has backed up 500km to the Second cataract within the Sudan. Evaporation from the artificial lake amounts to 5000 million cubic meters annually (about seven per cent of the lake's volume) and is causing unusual clouds and haze in the surrounding area, and even occasional rain.

But the lake also retains the silt that once renewed Egypt's fields. Chemical fertilizer plants running off the dam's hydroelectric power are filling that gap, while it is estimated that in 500 years' time the slit will have become available, or the wasteland to the south may have reverted to the lushness of long distant millennia. The water table beneath the Sahara has already risen noticeably as far away as Algeria. Though Egypt's population explosion and mistakes in economic policy have in some measure offset the dam's immediate benefits, it has already averted catastrophe.

The droughts that have brought starvation to Ethiopia and the Sudan have recently seen the Nile fall to its lowest level in 350 years, and the same scenes of famine would be repeated in Egypt were it not for the high Dam.

The British dam regulated the flow of the Nile during the course of the year; the High Dam can store surplus water over a number of years, balancing low floods against high and ensuring up to three harvests a year. The god Khnum has answered Zoser's prayer. The structure that achieves this contains the equivalent in material of 17 pyramids the size of the Great Pyramid of Cheops, and enough metal has been used in its gates, sluices and power plant to build 15 Eiffel Towers.

The road runs across the top back to the east bank. In merely driving along somehow the hugeness of the enterprise is lost upon you, and because it is ancient, and because it is functional and it works, it is easy not to be impressed. It is even possible for some to complain that was not worth the drowning of so many Nubian monuments. Some feeling for the controlled energy of the place is realized at the viewing platform over to the eastern end of the dam. The green water rises in eddies, like large bursting bubbles from somewhere below the visible tops of the sluices.

The generators hum as the river is put through its pace. Scores of lesser pylons flick currents of electricity towards the larger pylons striding across the desert, and bound by thick cables this energy is delivered into Egypt. Downstream, the Nile slips it harness and runs free beneath a glassy surface.