The dome altar is an open-air circular platform located on the central axis of the south side of the Temple of Heaven. It has three floors, and the railings and handrails are made of white marble. The ancients called one, three, five, seven and nine yang numbers, also called the sky, symbolizing the sky, and nine was the pole of yang numbers. The whole structure of Waqiu altar is a clever use of numbers, which embodies the connotation of China's philosophy. Altars, steps and railings all take multiples of nine or nine, which strongly conveys the connection between man and heaven. Standing on the Tianxin stone in the center of the highest floor of the ball altar, the sound of shouting or knocking will reverberate around. It is conceivable that in ancient times, emperors stood in the sky and prayed to the sky, and the echo produced was quite a dialogue between heaven and man.
There is also a magical legend about the construction of the ball altar. It is said that when Emperor Qianlong expanded the mound, he negotiated with his ministers to build it in multiples of 99, and craftsmen racked their brains to design the altar map of 99. As the deadline approached, a child in rags came to beg. The craftsmen kindly gave the child some food, only to see him wolf down, wipe his mouth with a rag after a full meal, throw it away and turn around and leave. The craftsmen picked up the rag and found an altar painted on it. Take a closer look, it is the 99 altar map. There are A Qin figures beside the design. It turns out that this child is a descendant of Qin, a great mathematician in ancient China. Although this is a legend, it embodies people's admiration for this beautiful building with accurate calculation and exquisite appearance, which conforms to both astronomical calendar and arithmetic principle. In fact, the ball field is only the representative of China's architecture in past dynasties, and there are countless buildings that perfectly unify art and science like it. They are the crystallization of the talents and skills of skilled craftsmen in Qian Qian, including the wisdom of ancient people in China.