The walls of Semneh were strengthened, both structurally and from a military point of view, by salient buttresses or small bastions on all the sides except that which faced the river. These buttresses were either twelve or thirteen in number and from six to eight feet wide at the top. In the re-entering angle which faces north-west there is a long diagonal buttress, by the use of which the engineer or architect at once economized material and protected a weak part of his structure in a most efficient manner. The salient angles of the _enceinte_ were protected by double towers, very well disposed so as to command the ditch. A symmetrical regularity is not to be found here any more than in the funerary and religious structures of Egypt. The curtain wall between two of the towers on the southern face is broken up into small buttresses of various degrees of salience, instead of being planned on a straight line like the rest. [Illustration: FIG. 32.--Siege of a fortress; from the Ramesseum, Thebes.] When the fortress was prepared for defence the parapets may have been furnished with wooden structures acting as machicolations, whence the besieged could cast javelins and stones and shoot arrows at an enemy attempting to scale or batter the walls. A bas-relief at Thebes which represents the siege of a fortress seems to indicate that the parapets were crowned by wooden erections of some kind (Fig. 32).[44] [44] Both the plate in the _Description de l'Égypte_ (_Ant._ vol. ii. pl. 31), and that in LEPSIUS (part iii. pl. 166), suggest this interpretation. The walls were surrounded by a ditch, which was from 95 to 125 feet wide. We cannot now tell what its depth may have been, but it appears to have been paved. The counterscarp and certain parts of the scarp were faced with stone, carefully polished, and fixed so as to augment the difficulty of approach. Moreover, the crown of the glacis and the wide glacis itself were also reveted with stone. All this formed a first line of defence, which had to be destroyed before the assailants could reach the place itself with their machines. The external line of the ditch does not follow all the irregularities of the _enceinte_, its trace is the same as that of the curtain wall, exclusive of the towers or buttresses. The clear width from the face of the latter is about sixty-four feet. Neither ditch nor glacis exist on the eastern face, where the rapids of the Nile render them unnecessary.