Circular Mound Altar  The Circular Mound Altar (圜丘坛 huán qiū tán) is an outdoor empty circular platform on three levels of marble stones, located in Beijing, China. It is part of the Temple of Heaven. It was constructed in 1530, during the 9th year of the Jiajing Emperor's reign in the Ming dynasty, and enlarged in 1749 (the 14th year of the Qianlong Emperor's reign in the Qing dynasty). The round terrace was first covered with deep blue glazed slabs surrounded with a white marble balustrade when it was expanded. It has a circular perimeter of 534m and a height of 5.2m  This altar was also built for religious purposes, especially for ceremonies to pray for rain by the emperor in times of drought. During the Ming and Qing dynasties (1368–1911 AD), the emperors would offer sacrifices to Heaven on the day of the Winter Solstice every year. Sacrificial animals and other offerings were burned here to ensure good harvests. A common animal slaughtered here was the bull, which the people would set on fire as a sacrifice of prosperity. This ceremony was to thank Heaven and pray that everything would be good in the future. Each wall represents something different. The round inner wall represents heaven while the square outer wall represents earth, according to Chinese beliefs and traditions. The three round white marble terraces that make up the altar represents communication with heaven. The Circular Mound Altar is special in the sense that the architecture of the place circulates around the number 9. To understand why the people of China back then chose the number 9, we must look at the concept Yin-Yang. In Yin-Yang, Yin represents the even numbers and Yang represents the odd numbers. 9, being the largest 1-digit odd number, is considered “extremely yang”. This number represents the Chinese Dragon, and the dragon represents the emperor. 9 is also said to symbolize, the “9 circles of heaven”. The number of pillars in each section is a multiple of 9. When we multiply this number by 4 to get the number of pillars for the whole circle, it would still be a multiple of 9. Also, the number of stone slates each wall is made of in the first terrace is 9. Each terrace has 9 slates. The top layer has 72 slates, the middle layer has 108 slates, and the bottom layer has 180 slates.