For the greater security of the corners of brick buildings, the Egyptians tilted the courses up at each end, thus building in a concave bed, with faces sloping inwards. This slope was copied in the stone-work, and is seen on the outsides of all Egyptian buildings (see fig. 83). The inside faces are always vertical, and this serves to distinguish the meaning of small portions of wall in excavations. [Illustration] [Illustration] Slight structures were made of palm-sticks, set upright, and lashed to a cross stick near the top, with other palm-sticks interwoven to stiffen the face, and the whole plastered with mud. Such construction is made now in Egypt, and is seen in the earliest figures of shrines. At the top the ends of the palm-sticks nod over, and form a fence to keep out intruders. This row of tops is the origin of the stone cavetto cornice, which always stands free above the level of the roof. At the corners the structure of palm-stick was strengthened by a bundle of sticks or reeds lashed round, and put as a buffer to prevent a blow breaking in the edge. This became the roll with lashing pattern which is seen down the edges of the stone buildings, and also beneath the cavetto cornice where it is copied from the line of sticks below the loose tops (see fig. 83). [Illustration] Another form of construction was with papyrus stems. These had a loose, wiry head like an _Equisetum_ or mare’s tail. When used for a cabin on a boat, the roofing stems were put through the loose head, which was tied above and below to hold them. Hence the row of heads became copied as an ornament along the tops of walls, and continued in use thus down to the latest times. The use of the arch was familiar from early times. Even before the pyramid-builders small arches of bricks were made. They were the general mode of roofing in the XIIth dynasty, when we see them drawn and imitated in stone. From the XIXth dynasty there remain the great arched store-rooms of the Ramesseum. Being of dried mud brick, which is far more easily crushed than stone or burnt brick, the circular form was not suitable, as the apex would yield by crushing. A more or less parabolic form was therefore used, so as to give a sharper curve at the top. To protect these arches from the weather, they were laid four courses thick, with a deep layer of sand and gravel over the top, to absorb any rain as a sponge. Arches were usually built without any centring; and to this day the Egyptian similarly builds arches and domes of any size without centring or support. Each ring of arch is laid on a sloping bed, so that the thin arch bricks on edge will stick in place by the mud-mortar until the ring is completed. The same construction is started in each corner of a room until the arching meets in a circle, when the dome is carried round ring on ring, increasing the dip toward the top. The successive coats of an arch are often bedded on opposite slopes, so that the rings cross each other.