As an ancient architectural structure of Chinese, the tai was a very much elevated terrace with a flat top, from which people can have a full sightseeing of a long distance outside and can enjoy the leisure and chat at will. Generally built of earth and stone and surfaced with brick, it was used as a belvedere from which to look into the distance. Nowadays, most of families have terraces at their home, and people take rest and enjoy the fresh air as well as the beautiful scenery of the platform or do activities in it. In fact, however, many well known ancient terraces as we know today are not just bare platforms but have some palatial halls built on top.
The tai could be built to serve different practical purposes. It could be used as an observatory, as for instance the one near Jianguomen in Beijing, with its brass astronomical instruments, can date to the Ming and Qing dynasties. It could also be used militarily, 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 meters, from which the garrison troops kept watch. On the track of the ancient Silk Road can still be seen, here and there, ruins of the old defence fortifications in the form of earthen terraces. A good example in hand is the Round City of the Beihai Park in Beijing. A terrace is five meters high, and it has, on its top space of 4,500 square meters, a main hall with side corridors.