Southern Dynasties and Song Dynasty (420-479).
"On Book Tables" is an important paper in the history of Chinese calligraphy theory and is considered to be the first relatively systematic work. Written by Yu He during the Southern Song Dynasty, it is of groundbreaking significance. This paper systematically elaborated and analyzed the expression form, technique and aesthetic value of calligraphy, and had a profound impact on the theory and practice of calligraphy in later generations. The exact period of creation of "On Book Tables" can be traced back to the Song Dynasty of the Southern Dynasty (420-479). This is one of the important milestones in the development of Chinese calligraphy theory.