This is the greatest engineering work of the kind ever constructed, and spans the Nile Valley at the head of the cataract basin. It is a mile and a quarter in length, and the river, which is raised in level about 66 feet, pours through a great number of sluice-gates which are opened or shut according to the season of the year and the necessities of irrigation or navigation. Behind, the steep valley is filled, and forms a huge lake extending eighty miles to the south, and many pretty villages have been submerged, while of the date-groves which surrounded them the crests of the higher trees alone appear above water. The green island of Philæ also is engulfed, and of the beautiful temple of Isis built upon it only the upper portion is visible. Below the dam activity of many kinds characterizes the Nile, as does the sound of rushing water the Cataract basin. Above, silence reigns, for the huge volume of stored water lies inert between its rugged banks. One's first thought is one of sadness, for everywhere the tree-tops, often barely showing above water, seem to mourn the little villages and graveyards which lie below, and as yet no fresh verdure has appeared to give the banks the life and beauty they formerly had. As at the cataract, here also the hills are simply jumbled heaps of granite boulders, fantastically piled one upon the other, barren and naked, and without any vegetable growth to soften their forbidding wildness. On many rocky islands are the ruined mud buildings of the Romans, and more than one village, once populous, lies deserted and abandoned upon some promontory which is now surrounded by the flood. Though a general sense of mournfulness pervades it, the scenery has much variety and beauty, nor have all the villages been destroyed; many had already been built far above the present water-level, while others have sprung up to take the place of those submerged. These again present new features to the traveller, for, unlike many we have seen below the cataract, these Nubian dwellings are well built, the mud walls being neatly smoothed and often painted. The roofs are peculiar, being in the form of well-constructed semicircular arches, all of mud, and in many cases the tops of the outside walls are adorned by a kind of balustrade of open brickwork. Half hidden among the rocks the native house has often the appearance of some temple pylon, and seems to fit the landscape in a peculiar way, for no form of building harmonizes so well with the Egyptian scenery as the temple. Whether or not the native unconsciously copies the ancient structure I cannot say, but anyone visiting Egypt must often be struck by the resemblance, particularly when, as is often the case, the little house is surmounted by pigeon-cotes, which in form are so like the temple towers.