Geometric Tiles, Mosque of Moulay Idriss, Morocco
Islamic decoration makes great use of geometric patterns which have developed over the centuries. Many of these derived from various earlier cultures: Greek, Roman, Byzantine, Central Asian, and Persian. They are usually distinguished from the arabesque, the term for decoration in Islamic art based on curving and branching vegetal forms. But sometimes foliage and linear geometric patterns are combined in a single design, and some purely abstract linear patterns adopt designs that seem clearly derived from vegetal arabesque ones. The geometric designs have evolved into beautiful and highly complex patterns, still used in many modern day settings.
The square and rectangle play a significant role in Islamic architecture. Some of the reason for this is facades built from rectangular bricks. This ornamental brickwork casts shadows in the strong desert sunlight and creates a three-dimensional effect. A recurring motif is a small central square turned 45 degrees within a larger square. Another source for the square motif is woven baskets.
The Persianate world is the main area with buildings with decorative brickwork, especially during the Seljik period; the Great Mosque of Cordoba is another example further west. The eight-pointed star is another common motif in Islamic architecture, often found in tile-work and other media. Star patterns are extremely complex when the outer points are joined together and other intersections connect in a systematic way. The Alhambra palace in Granada, Spain is a famous example of repeating motifs which occur in the tile and stucco decoration. Octagons appear in Islamic architecture in various shapes. They frequently occur in marble floors. The Citadel of Aleppo in Syria contains marble opus sectile floors, which utilize the square and the eight-pointed star. Pierced screens (jali in India) are another common location for geometric decoration. - wikipedia