"Throughout history Islamic art in religious contexts has traditionally involved the creation of complex geometric designs which are said to create the impression of unending repetition and is believed to be associated with the infinite nature of God. The absence of figural imagery is typical of art associated with religious buildings and artefacts.
The circle, and its centre, are the point at which all Islamic geometric patterns begin. The circle symbolically represents one God, eternity, without beginning and without end. The circle is the most beautiful parent of all polygons, both containing and underlying them."
For more of the above, and a look at how these designs may be developed from basic shapes, check out
this Islamic geometric art page.