The leading principle in the construction of fortress-gates was always the same, but the details varied according to the taste of the engineer. At the south-east gate of the fort of Abydos (fig. 30) the _place d'armes_ between the two walls is abolished, and the court is constructed entirely in the thickness of the main wall; while at Kom el Ahmar, opposite El Kab (fig. 31), the block of brickwork in the midst of which the gate is cut projects boldly in front. The posterns opening at various points facilitated the movements of the garrison, and enabled them to multiply their sorties. [Illustration: Fig. 32.--Plan of the walled city at El Kab.] The same system of fortification which was in use for isolated fortresses was also employed for the protection of towns. At Heliopollis, at Sãn, at Sais, at Thebes, everywhere in short, we find long straight walls forming plain squares or parallelograms, without towers or bastions, ditches or outworks. The thickness of the walls, which varied from thirty to eighty feet, made such precautions needless. The gates, or at all events the principal ones, had jambs and lintels of stone, decorated with scenes and inscriptions; as, for instance, that of Ombos, which Champollion beheld yet _in situ_, and which dated from the reign of Thothmes III. The oldest and best preserved walled city in Egypt, namely, El Kab, belongs probably to the ancient empire (fig. 32). The Nile washed part of it away some years ago; but at the beginning of the present century it formed an irregular quadrilateral enclosure, measuring some 2,100 feet in length, by about a quarter less in breadth. The south front is constructed on the same principles as the wall at Kom es Sultan, the bricks being bedded in alternate horizontal and concave sections. Along the north and west fronts they are laid in undulating layers from end to end. The thickness is thirty-eight feet, and the average height thirty feet; and spacious ramps lead up to the walk upon the walls. The gates are placed irregularly, one in each side to north, east, and west, but none in the south face; they are, however, in too ruinous a state to admit of any plan being taken of them. The enclosure contained a considerable population, whose dwellings were unequally distributed, the greater part being concentrated towards the north and west, where excavations have disclosed the remains of a large number of houses. The temples were grouped together in a square enclosure, concentric with the outer wall; and this second enclosure served for a keep, where the garrison could hold out long after the rest of the town had fallen into the hands of the enemy. [Illustration: Fig. 33.--Plan of walled city at Kom Ombo.] [Illustration: Fig. 34.--Plan of fortress of Kùmmeh.] [Illustration: Fig. 35.--Plan of fortress of Semneh.] [Illustration: Fig. 36.--Section of the platform at A B, of the preceding plan.]