The temple consists of two parts--the inner altar and outer altar. The main buildings are in the inner altar, on the north-south axis. At the southern end are the Imperial Vault of Heaven(1) and the Circular Mound Altar(2). On the northern end are the Hall of Prayer for Good Harvests(3) and the Hall of Imperial Zenith(4). The structures at both ends are connected by a 360-meter-long walk. There is also the Hall of Abstinence(5) inside the West Heavenly Gate in which the emperor fasted for three days and bathed before prayer.
The temple's main building is the Hall of Prayer for Good Harvests, where the emperor prayed for good harvests. The round hall, 38 meters high and 30 meters in diameter, has triple eaves and a cone-shaped deep blue tile roof crowned with a gilded knob. Surrounding the hall is a six-meter-high spacious circular stone terrace on three levels, each edged by a balustrade of carved white marble.
The Circular Mound Altar is one of the more important buildings and is a three-tier white stone terrace enclosed by two walls. Geometrically designed, the altar has a taiji rock at the center of the top terrace. If you stand on the rock and speak in a normal voice, your voice will sound louder and more resonant to yourself than to others around you, because the sound waves reflected by the balustrades are bounced back to the center by the round wall .
The Imperial Vault of Heaven, the place to lay the memorial tablets to the heaven is to the north of the Circular Mound Altar. It is very similar in structure to the Hall of Prayer for Good Harvests but is smaller. The Vault, made of brick and timber, is 19 meters high and 15.6 meters in diameter. It is surrounded by a circular wall of polished brick with an opening to the south. This is known as the Echo Wall(6) and is 3.72 meters high, 61.5 meters in diameter and 193 meters in circumference. If a person whispers close to the wall at any point, his voice can be heard distinctly at any other point along the wall.
Around the Hall of Abstinence are two imperial ditches and they are circled by a 163-bay walkway. The Abstinence Bronze Man Pavilion and Time and Memorial Tablets Pavilion are at he Celestial Terrace of the main hall. To add the solemnity of the occasion, the bells in the two bell towers at the northeast end were struck when the emperor prayed for good harvests.
Notes:
1. the Imperial Vault of Heaven 皇穹宇
2. the Circular Mound Altar 圜丘壇
3. the Hall of Prayer for Good Harvests 祈年殿
4. the Hall of Imperial Zenith 皇乾殿
5. the Hall of Abstinence 齋宮
6. the Echo Wall 回音壁
