Terrace (Tai)
The tai was an ancient architectural sturture, a very much elevated terrace with a flat top. Generally built of earth, stone and surfaced with brick, they are used as a belvedere from which to look into the distance. In fact, however, many well-known ancient tai as we know it today is not just a bare platform but has some palatial halls built on top.
A good example is the Round City of the Beihai Park in Beijing. A terrace five metres high, it has an area of 4, 500 square metres on its top and a main hall with side corridors.
The tai could be built to serve different practical purposes. For example, it could be used as an observatory as is the one near Jianguomen in Beijing which dates back to the Ming and Qing dynasties. It could also be used for military purposes like the beacon towers along the Great Wall, to transmit urgent information with smoke by day and fire by night. Also on the Great Wall, there is a square tai at intervals of every 300 to 400 metres from which the garrison troops kept watch. On the track of the ancient Silk Road, ruins of the old defence fortifications in the form of earthen terraces can still be seen.