Originally built in the 17th century, the citadel at Quảng Trị was substantially repaired in 1809 by the first Nguyễn king Gia Long (1802-1819) to fortify the northern approach to his capital at Huế. It remained an earth structure until 1827 when Gia Long's son Minh Mạng (1820-1840) replaced the earlier structure with a new four-sided fortress in Vauban style, featuring 5 metre high walls, four gates with watchtowers and a 20 metre wide moat. It was here that King Hàm Nghi stayed in 1883 during his brief resistance war against the French. The colonial government later built a prison inside its walls which housed several leading revolutionaries, including future Party General Secretary Lê Duẩn. However, notwithstanding its long history the citadel is chiefly remembered today as the venue for one of the bloodiest battles of the American War. During the battle of Quảng Trị (28 June-16 September 1972) most of Quảng Trị town was razed to the ground and the citadel was almost completely destroyed. Today only a few isolated sections of the citadel remain; bomb craters may still be seen in the southern section of the citadel, which has been left untouched to commemorate the 81-day battle. A war martyrs’ monument has also been erected at the centre of the site in tribute to those who died here and a Quảng Trị Citadel Museum erected on site.