Kinh Thanh Hue (Hue Capital Citadel) construction started in 1805 under the reign of Emperor Gia Long and completed in 1832 under the reign of Emperor Ming Mang. Under Nguyen' reign, Kings have ordered to build ramparts, palaces and constructional works of royal. Over 200 years to now, it is still original with nearly 140 small and large constructions. The Citadel, square in shape and almost 10 km in circumference, 6 m high, 21 m thick and 10 entrances. On the top of the walls that surround it, 24 bastions are established for defensive purposes. Besides, the Citadel has an ancillary gate connecting the Tran Binh Bastion called the Thai Binh Mon (Peace Gate).