Turkey has a rug-making tradition as old as Persia's. Turkish rugs are mainly based on geometric motifs, frequently of a prayer niche design. The colors most frequently used are red and blue. Green, their sacred color, is used on prayer rugs. There are four types of Turkish rugs; they are classified according to the materials used. The categories include: Silk on silk, Wool on cotton, Wool on wool, Viscose on cotton, Kilims, Tulu, and Anatolian Turkish Rugs.