By the Tang dynasty, tombs were being made in the shape of turtles. The symbol of the eight diagrams, commonly used among Chinese as a charm, was derived from the strong and simple lines found on turtle shells.
唐代起，中國人的墓葬已砌成龜狀，中國社會重要的護身符八卦，更依樣畫葫蘆自龜背上線條樸拙有力的圖案。