Geometria e figurazione nelle decorazioni murarie di Tozeur e Nefta (Tunisia)

The study of the geometric patterns characteristic of the wall faces present in the oasis cities of Tozeur and Nefta, located on the northern edge of the salt lake Chott el Jérid (Tunisia), is the theme of this paper. The traditional construction system in use in this desert region of Tunisia includes brickwork in raw earth mixed with straw, packed in bricks (adobe) or poured directly into a wooden formwork (pisé), covered on both sides with clay bricks baked in the sun and then in the oven. Brick as a decorative element is laid slightly protruding from the plane of the masonry. The exclusive use of brick represents a limit to figuration; a further limitation is constituted by the fact that the brick is always placed in line with the wall texture, and therefore exclusively horizontally and/or vertically. From this it follows that the inclined lines in the drawing can only be obtained by staggering the bricks themselves and have a serrated pattern. All the external and internal facades of traditional houses have complex decorative panels, especially at the entrances and on the external front of the bortals, characteristic porticoes of both cities. The extreme simplicity of the brick has not limited the creation of countless decorative motifs, generated from elementary figurations which, through variations, allowed the development of an extremely rich formal vocabulary. The figures used in Nefta and Tozeur, oasis-cities only 25 kilometers away, are the same, except for a particular design called zarbiya, present exclusively in Nefta. Almost all the patterns derive from the rhombus and the octagon (except the shetrouàni, horizontal band, and the vertical column), through operations of section, rotation, and overturning. The herringbone pattern, for example, can be considered as composed of a portion of rhombus; the one called bu habibi is composed of a rhomboid shape (maqrudha) sectioned along the horizontal axis and repeatedly placed side by side. From a figurative point of view, we can identify nine patterns that refer to elements present in the daily life of the oasis: three depict the camel, two the snake, one the shear, one the nightingale (more precisely: its nest) and two the Palm. The rest are abstract figurations. The method applicable to the study of the wall decorations present in the two main city-oases of the Chott el Jérid was developed starting from the geometric analysis of the minimal elements; this was followed by the study of aggregative methods and the reconstruction of the abstraction process that led to the formalization of the patterns that represent real elements.