Son Tay ancient citadel was built by King Minh Mang in 1822 to defend the western gateway to the city of Thang Long, which is now, of course, Hanoi.

Son Tay ancient citadel is located between Son Tay town, distance center of Hanoi than 40km. This is an ancient military architecture, was built in the reign of King Minh Mang in 1822. It has the style of a Vauban fortification and in time French architects praised it as a masterpiece of Vietnamese architecture.

There were four main gates also made of bee-stone (laterite), the special material from Xu Doai. The citadel was where the kings of the Nguyen Dynasty lived and worked when in the area.Citadel have quadrilateral, trapezoidal cross-sections, sincere 6m wide, 4 meters wide aspects into, there are many holes in the top to the soldiers hiding out in shooting or stabbing spears are long enemy when they climb the walls.

The four main ports: The south gate called Tien gate; the north is the Hau port, the East main and West main.

 Vong Lau:

Each port on the top is guard floor (Vietnamese call Vong Lau) and only one entrance, the outside is covered Duong Ma Thanh (also known as fish bearing) the cone shape of the outer barrier.

Around the outer moat and deep 3m, wide 20m, long 1.795m, is connected to the Tich river in the southwest corner.

The outer ring is far from La Thanh (the citadel outside) is covered by land high 3.5m, pentagon, external spines dense bamboo cover. The four external ports also open look to the four directions: East, West, South, North, now called La Thanh street.

Vong Cung:

In the citadel, the important works are built on the symmetry center axis North-South. The middle is the "Vong Cung Nu" to the south, where take a rest of the King when going to inspect provinces governed by viceroys each week. Spring and Autumn period, to sacrifice whenever reference only King confer.

Before Kinh Thien palace is a large tiled courtyard, outside the radiation portal is built of brick, bank relief  "Long Van Khanh Hoi" with lime mortar. Next is the "Doan Mon" has three doors, straight into the Ky Dai (flagpole) built on a square base pyramidal laterite about high 18m.

To the west is Vo Mieu, places of worship and the generals had died while bravely fighting to protect citadel. At the four corners of  citadel, the past four wells to the square, built of stone steps down to the bottom of bees, about deep 6 meters, year-round food supply for troops in the townships and people in the citadel.

The middle of  citadel is the ancient flag tower is painted bright red and new stones are now where moss-covered ones used to be.

 After nearly 200 years, been many wars and devastating time, ancient Son Tay citadel  largely destroyed, leaving only the walls, doors, money, door post, two cannons, the foundation of Kinh Thien palace, the wells ... 

  You can find two ancient gates under hundred-year-old trees.

Son Tay ancient citadel is coved by green trees.There is the moat that surrounds ancient citadel.  It's really quiet and cool for walking.

Son Tay citadel should be one of the great symbols of Vietnam’s cultural heritage together along with Co Loa ancient citadel, Hanoi citadel and Hue Imperial palace.