The citadel was constructed by 30,000 labourers in 1790 in Tan Khai village. It was designed by Olivier and Le Brun. It looked a lotus with 8 gates on 3 roads. From East to West, South to North was 648.55 meters of length, its wall was 6.334 meters of high, its ditch was 6.821 meters of deep and 75.525meters of large. It bound by 4 streets: Dinh Tien Hoang (East),Nam Ky Khoi Nghia (West), Le Thanh Ton (South), Nguyen Dinh Chieu(North).
The citadel built of Bien Hoa granite, bricks. In citadel had principal offices and monuments such as Royal ancestors’ temple, Rice store, weapon store, ship working shop, mandarin post… From the citadel there were three important long roads to North, West and Cambodia.