The three-tiered marble terrace is shaped like the Chinese character "earth", and the three big Halls are located there. The marble terrace is 8. 13 meters high in the center, 7.12 meters at the edge, and it's easy for draining off rain water. The terrace is encircled by 458 marble balusters with dragon and phoenix designs carved on them. At the edge of each terrace, there are 1, 142 marble waterspouts in the shape of mythical monsters or dragon's heads, which would spout gushes of water during heavy rain and served as both decorations and rainspouts. They really demonstrate a perfect combination of the practical with the arts. When it rains, people can see a beautiful view of “thousands of dragons spouting water”.

Each marble terrace is higher than the other, on which stand three main buildings of the outer palace; they are: the Hall of Supreme Harmony, the Hall of Complete Harmony, and the Hall of Preserving Harmony which are all lying on the north-south axis. The three big buildings were first built in 1420, but unfortunately they were burnt down by lightning. Not until in 1439, did the sixth Ming emperor decide to rebuild the three big halls on the original site. But after that, they were struck down again, and were rebuilt and renovated many times. The present halls were rebuilt in 1695 by the Qing emperors.

In the middle of the terrace, you can find three staircases leading to the Hall of Supreme Harmony. The central staircase with a long stone ramp in the middle, carved with dragons and clouds, was exclusively for the emperor in the old days. During a ceremony, the marble ramp would be covered with red carpet and the emperor was carried up the center of the ramp in a sedan chair. The officials and royal family members had to climb the steps on either side.