[Illustration: FIG. 29.--Military post. Plan of the entrances; from Mariette.] The most curious relic of the military engineering of the Egyptians is to be found in Nubia. Thirty-seven miles south-ward of the cataracts of Wadi-Halfah the Nile has worn a channel through a long chain of granite hills which run across the valley from east to west. On each side of the river-bed these hills rise to some height and across its torrent there are a few detached rocks, which once formed a natural dam, but between which the water now rushes impetuously. Navigation is only possible among these rapids during the inundation. This point in the river's course was therefore well fitted to be the gate of Egypt and to be fortified against the incursions of the southern tribes. During the first Theban Empire, the Pharaohs of the twelfth dynasty drew the national frontier at this point, and resolved to establish themselves there in force. The Third Ousourtesen seems to have built the two fortresses of which substantial remains exist even now. Each fortress contained a temple and numerous houses. Lepsius gives the name of _Kummeh_ to that on the right bank and reserves the name _Semneh_, which has usually been applied to the whole group, to the building on the left bank only. [Illustration: FIG. 30.--Bird's-eye view of the fortress of Semneh; restored by Charles Chipiez.] For our restoration (Fig. 30) we have had to depend very little upon conjecture.[42] The only flight of fancy in which we have indulged is seen in the extra height which we have given to the tower at the north-eastern angle of the building. It seemed to us probable that at some point upon such a lofty terrace there would be a belvedere or watch-tower to facilitate the proper surveillance of the country round about. For the rest we have merely re-established the upper part of the works and restored its depth to the ditch, which had been filled in by the falling of the parapets. The line of walls and bastions can be easily followed except at one point upon the southern face, where a wide breach exists. The destruction of this part of the wall alone and the clearing of the ground upon which it stood, suggests that it was broken down by man rather than by time. It is probable that the fortress was taken by some Ethiopian conqueror, by Sabaco or Tahraka, and that he took care to render its fortifications useless in a way that could not be easily repaired.