to the walls with a mortar or grout. In the case of the Almohad tilework on the minarets of the Kutubiyya and Kasbah Mosque in Marrakesh, the tiles were nailed to a wooden framework set into the surface of the wall behind them. Forms and patterns In traditional zellij decoration, geometric patterns of varying complexity were the most prominent and widespread motif. Vegetal arabesque motifs were also used, though less frequently. Geometric patterns were created on the basis of tessellation: the method of covering a surface with the use of forms that can be repeated and fitted together without overlapping or leaving empty spaces between them. These patterns can be extended infinitely. In Islamic art, the most important types of tessellation in geometric motifs are based on regular polygons. This form of expression within the conceptual framework of Islamic art valued the creation of spatial decorations that avoided depictions of living things, consistent with taboos of aniconism in Islam on such depictions. Traditions of mosaic tilework were also prevalent across various periods in other parts of the Islamic world, including Iran, Anatolia, and the Indian subcontinent. Whereas in the eastern Islamic world blues and turquoises were the dominant colours, in western zellij yellows, greens, black, and light brown were very common, with blues and turquoise also appearing in the mix, and they were typically set against a white ground. In western Islamic art, under the Nasrid and Marinid dynasties, a great variety of geometric patterns were created for architectural decoration. Among the most common was a pattern employing six-pointed and twelve-pointed star compositions, with eight-pointed stars inserted between them. A popular trend was the use of patterns based on systems of fourfold symmetry. This family of patterns was widely used in other Muslim cultures further east, but in the Maghreb and al-Andalus artists excelled at their use and introduced several innovations. One innovation was to make the repeating unit of the patterns larger, with broader compositions involving many different polygonal forms. Other innovations were the incorporation of more complex sixteen-pointed stars into some of these patterns and the insertion of further "arbitrary" design elements within the wider patterns. These innovations not only increased the complexity of the motifs but also increased their visual diversity. The family of patterns involving fivefold symmetry, which was widely used and developed throughout the rest of the Islamic world, was less common in the Maghreb