Why is Yan Zhenqing's calligraphy a treasure?

Yan Zhenqing's calligraphy is a must in China's calligraphy circle, and Yan Zhenqing's calligraphy realm is very high all his life. He studied calligraphy for a long time before he was fifty years old, and he had a high accomplishment in calligraphy and established his own style, which was the early stage of Yan Zhenqing's calligraphy system. Later, Yan Zhenqing learned Zhang Xu's strong points, combined Zhang Xu's brushwork with his own style, and began the sharpening stage of calligraphy, retaining a large number of inscriptions. After the Anshi Rebellion, Yan Zhenqing took part in the counter-insurgency and temporarily put down his calligraphy. Later, after the Anshi Rebellion was put down, Yan Zhenqing's calligraphy gradually matured, with both form and spirit, and it was very imposing, and Yan Zhenqing's calligraphy gradually began to emerge. After the age of 65, Yan Zhenqing's calligraphy has completely entered a superb stage, revealing a heroic and powerful feeling in its roundness. Therefore, Yan Zhenqing's Yan School calligraphy is a treasure in China calligraphy circle.