Construction of the moated Citadel(Kinh Thanh)was begun in 1805 & finished in 1832.The number of labours working in 1 day was sometimes up to 80,000. The Citadel's area is 520 ha., perimeter is 10 km and the shape is almost square. The wall is 6.6 metres high and 21 metres thick. The two surfaces of the wall are made by bricks and the inner part is made by earth. There are 10 entrance gates. Around the Citadel is a system of rivers for protecting the Citadel.