Why do calligraphy lovers of all ages regard the Monument to the Immortal Prince as a treasure of calligraphy art?

There are 33 lines of inscriptions, each with 66 words. Running script and cursive script alternate with each other and approach cursive script. Famous calligraphers in the Tang Dynasty, Xue Ji and Zhong Shaojing, wrote the inscriptions You Xian Pian and You Xian Pian. Calligraphy lovers throughout the ages regarded the Monument to the Immortal Prince as a treasure of calligraphy art.