Constructed in the ninth year of Emperor Jiajing’s reign (1530), the altar served as a place for holding the ceremony of worshipping Heaven at the winter solstice every year, hence popularly known as the Heaven-Worshiping Terrace. It was originally a round terrace covered with deep blue glazed slabs and then changed into a terrace with light green stone slabs and white marble balustrades when it was expanded in the 14th year of Emperor Qianlong’s reign (1749).
The numbers of steps of each leading flight, the slabs of each tier, and the balustrades are nine or nine multiples, symbolizing the Nine Heavens and emphasizing its supreme importance.
