The Hall of Celestial and Terrestrial Union was the throne room of the empress, where she would receive guests or meet with the concubines, princesses and the wives of the princes.
It was created during the reign of Jiajing of the Ming dynasty, and was twice restored, in 1655 and 1669. In 1797, it was damaged by a fire and rebuilt the following year. The building has a single roof, topped with a spherical, gilded bronze pinnacle.
It is square and smaller than the Hall of Central Harmony, but it is built in the same architectural style.
Inside, you can see two very unusual clocks. One is mechanical, built in wood in 1798, shaped like a Chinese pavilion and almost six meters tall. There are steps at the back, and if you wind it up, you can listen to its marvelous carillon.
The other is a bronze water clock, built in 1745 and based on technology that measures time using the flow of water, invented in China over 3000 years ago.
