Due to the introduction and spread of Vairocana thought of Avatamsaka Buddhism，the physical characteristics of the Tun-huang Mo-kao grottos (敦煌莫高窟) and their images during the post Sui (隋)and T'ang (唐) periods underwent major changes. Images inside the grottos were characterized by their iconographic meanings of mutual interpenetration and non-obstruction，resulting in a variety and an abundance of images on the grotto walls. Additonally，a holistic and unifying connection among these different images was not lost. This led to the development and evolution of the symmetry that characterizes the grotto images after the mid-T'ang (中唐) period which was a complete change from the singular characteristic of those images of the Northern Wei (北魏) period based on Nirvana thought. Since the Northern Wei period，the physical appearance of the grotto images were characterized by the "central axis, " a symbolism of the substance of Nirvana thought. Afterwards, there occurred the transformation into the structure of the "central mandala, " a symbolism of the "one in all，all in one" ideology of Avatamsaka thought. This establishment of the T'ang period Tun-huang grottos provided room later on for the development of ritualism including repentance rites, esoteric practice，and so on.
