The Citadel of Saigon (Vietnamese: Thành Sài Gòn [tʰâːn ʂâj ɣɔ̂n]) also known as the Citadel of Gia Định (Vietnamese: Thành Gia Định; Chữ Hán: 嘉定城 [tʰâːn ʒaː dîˀn]) was a late 18th-century fortress that stood in Saigon (also known in the 19th century as Gia Định, now Ho Chi Minh City), Vietnam from its construction in 1790 until its destruction in February 1859. The citadel was involved in two wars prior to its destruction, first when it was captured by Lê Văn Khôi in 1833 and used in a revolt against Emperor Minh Mạng, then recaptured in 1835. In 1859, it was captured following a French naval bombardment and then destroyed, as part of the colonization of southern Vietnam which became the French colony of Cochinchina.
In the late 18th century, the city of Saigon was the subject of warfare between the Tây Sơn dynasty, which had toppled the Nguyễn lords who ruled southern Vietnam, and Nguyễn Ánh, the nephew of the last Nguyễn lord. The city changed hands multiple times before Nguyễn Ánh captured the city in 1789. Under the directions of French officers recruited for him, a Vauban style "octagonal" citadel was built in 1790. Thereafter, the Tây Sơn never attacked southern Vietnam again, and the military protection allowed Nguyễn Ánh to get a foothold in the region. He used this to build an administration and strengthen his forces for a campaign that united Vietnam in 1802, resulting in his coronation as Gia Long.
In 1833, his son Minh Mạng was faced with a rebellion led by Lê Văn Khôi, which started after the tomb of Khôi's father Lê Văn Duyệt was desecrated by imperial officials. The rebels took control of the citadel and the revolt continued until the imperial forces retook control of the citadel in 1835. Following the capture of the citadel, Minh Mạng ordered its razing and replacement with a smaller square stone-built structure, that was more vulnerable to attacks. On February 17, 1859, the citadel was captured during the French invasion after less than a day of battle and significant amounts of military supplies were seized. Realising that they did not have the capacity to hold the fort against Vietnamese attempts to recapture it, the French razed it with explosives, before withdrawing their troops.
Central Vietnam was ruled by the Nguyễn lords, who had broken away in the early 17th century from the Trịnh lords, who ruled the north. The Nguyễn continued the southward expansion that eventually reaching the Mekong Delta. The southern edge of Vietnam, being further away from the Nguyễn power base in the centre, was loosely governed.
In 1771, the Tây Sơn rebellion erupted from Bình Định Province. In 1777, the last of the Nguyễn lords was deposed and killed. His nephew Nguyễn Phúc Ánh was the most senior member of the Nguyễn family to have survived the Tây Sơn victory and conquest of Saigon in 1777. Nguyễn Ánh fled to Hà Tiên in the far south of the country, where he met Pigneau de Behaine, a French priest who became his adviser and played a large part in his rise to power. Over the next few decades, there were continuous attacks and counterattacks by both sides and Saigon changed hands frequently. Eventually, Nguyễn Ánh was forced into exile at Bangkok. The Tây Sơn regularly raided the rice growing areas of the south during the harvesting season, confiscating the Nguyễns' supply of food.
In 1788, the Tây Sơn moved north to attack the Trịnh and unite Vietnam. Nguyễn Ánh took advantage of the situation to return to southern Vietnam. After rebuilding his army, he recaptured Saigon on September 7, 1788. His grip on the south was enhanced by a group of Frenchmen and equipment that Pigneau had recruited, although the magnitude of the aid has been the source of dispute.
Having seen Saigon slip from his hands on many occasions in the previous decade, Nguyễn Ánh was keen to strengthen his hold on the key southern city, turning it into his capital, and the base for his preparations for his planned conquest of the Tây Sơn and Vietnam. His enemies had regularly raided the area and confiscated the rice harvest.
The French officers recruited by Pigneau were used to train Nguyễn Ánh's armed forces and introduce their technological expertise to the war effort. Olivier de Puymanel was responsible for the construction of fortifications. One of Nguyễn Ánh's first actions was to ask the French officers to design and oversee the construction of a modern European-style citadel in Saigon. The citadel was designed by Theodore Lebrun and de Puymanel and 30,000 people were used to construct it in 1790. The townfolk and their mandarins were heavily taxed for the work, and the labourers were worked to the extent that it provoked a revolt.
The stone and earth citadel eventually had a perimeter measuring 4,176 m (13,701 ft) in a Vauban model. It was described as being of a Chinese style, designed in the octagonal form of a lotus flower, with eight gates in the Đại Nam nhất thống chí, the official records of the Nguyễn dynasty. However, such records are believed to have been written metaphorically, rather than literally. Two French maps of the city, drawn by de Puymanel and Jean-Marie Dayot—another senior officer—in 1799 and 1815 respectively, show a square-shaped design, with four main towers at the corners, and six outer half-towers, centered at 10°46′58″N 106°41′53″E. Louis Malleret said that "it is impossible to see any octagonal design in this".
The design suggested by the French maps is corroborated by the accounts of British and American visitors who travelled to Saigon seeking trade deals for their respective countries in the 1820s. British trade envoy John Crawfurd wrote that "the citadel of Saigon...is, in form, a parallelogram...I conjecture, from appearance, that the longest side of the square may be about three-quarters of a mile in length". George Finlayson, a naturalist and surgeon who travelled to southern Vietnam as a member of a trade delegation from the British East India Company, described the fortress as being "of square form, and each side is about half a mile in extent". Lieutenant John White of the United States Navy, travelling as a trade envoy for the United States, claimed to have seen only four of the eight gates, but Crawfurd wrote that "With the exception of the four principal gateways...the gates consist of four large and as many small ones". The four small gates observed by Crawfurd are in accord with the design principles of Vauban.
The two French maps of the citadel show a Vauban structure, as do the accounts of the trade delegates. According to Crawfurd, "the original plan appears to have been European, but left incomplete. It has a regular glacis, an esplanade, a dry ditch of considerable breadth, and regular ramparts and bastion...The interior is neatly laid out and clean, and presents an appearance of European order and arrangement." Finlayson described the citadel as having been "constructed of late years, on the principles of European fortification. It is furnished with a regular glacis, wet ditch, and a high rampart, and commands the surrounding country." Lebrun and de Puymanel did not choose the site for the citadel, instead using the compound of a fort. The location was seen as ideal for such a purpose. It was of substantial elevation, with three sides bordered by natural waterways at right angles: the Saigon River, Arroyo Chinois and the Arroyo de l'Avalanche. Crawfurd reported that the walls were made of earth that was "covered everywhere with a green sward". White estimated that the height of walls was around 6 m (20 ft). According to Crawfurd, the gateways were built from stone and lime, with the towers being of Chinese architecture with a double-canopied appearance. The approach towards the gates include a zig-zag in the glacis.
The location was in complete fulfilment of the requirements of geomancy, with a north-west/south-east orientation. The three courses of water provided the "vital energy". As three waterways formed right angles, the square structure was the most suitable. The aspect of the citadel closest to a Chinese style was the decoration of the gates, which Finlayson noted as "handsome and ornamented in the Chinese style". White recalled that the gates were reinforced by iron, a style that was common in Europe. The citadel was bordered on three sides by pre-existing waterways, increasing its defensive capacity.