The citadel was built in Vauban architectural style under King Minh Mang’s dynasty. It used to be the capital of three provinces of Son Tay, Hung Hoa and Tuyen Quang in the Nguyen Dynasty.

The citadel was the base of military of the Nguyen Dynasty against the French in the 1870-1880s. It was lost to the French in 1883.

Son Tay ancient citadel is in square shape, with 400m long sides, totaling around 16 hectares in area. Its four gates face East, West, South and North. It was built from laterite, with walls of 4.5-5 meters long. There is a 3m deep, 20m wide and 1795m long moat outside the wall, which is connected to the Tich Giang river.

At present, two gates have been damaged. They are being restored. So far, three preservation projects have been carried out in 1995, 2001-2005 and one since late 2009.

The citadel in pictures: