What is an ancient observatory and when was it built?

In the third millennium BC, there were one or more mountain platforms or rooftops in the main temples of almost every city.

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Beijing Ancient Observatory is a national key cultural relic protection unit, located in the southwest corner of Jianguomen overpass in Beijing. Founded in the Yuan Dynasty, it was originally named "Four Tiantai". When Beijing was conquered in the early Ming Dynasty, it was destroyed by war, and the remaining astronomical instruments were transported to Nanjing for preservation. This station was rebuilt in the next seven years (1442). The ancient observatory is a high-rise brick building rebuilt in the southeast corner of Dadoucheng in Yuan Dynasty. Renamed "Stargazing Platform" and copied a set of instruments. In the Ming Dynasty, there were large bronze astronomical instruments such as armillary sphere, simple instrument and astrolabe. Under the stage, there were buildings such as Wei Zi Hall, Leaky Pot Room and Qing Ying Hall, with watches and leaky pots built in.

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