Tân Sở citadel was a secret military base in central

Vietnam Vietnam, officially the Socialist Republic of Vietnam (SRV), is a country at the eastern edge of mainland Southeast Asia, with an area of about and a population of over 100 million, making it the world's List of countries and depende ...

that was built in the 1880s. It was built up by

Tôn Thất Thuyết Tôn Thất Thuyết ( 尊室説; 12 May 1839 in Huế – 1913 in Longzhou), Courtesy name Đàm Phu (談夫), was the regent and leading mandarin of Emperor Tự Đức of Vietnam's Nguyễn dynasty. Thuyết later led the Cần Vươn ...

, the regent of the

Nguyễn dynasty The Nguyễn dynasty (, chữ Nôm: 茹阮, chữ Hán: 朝阮) was the last List of Vietnamese dynasties, Vietnamese dynasty, preceded by the Nguyễn lords and ruling unified Vietnam independently from 1802 until French protectorate in 1883 ...

, in preparation for an uprising against French colonialism.Oscar Chapuis -The Last Emperors of Vietnam: From Tu Duc to Bao Dai - 2000 Page 20 "Inside the citadel, Thuyet had buried half of the imperial treasury, including 300,000 taels of gold and only Tuong' s opposition prevented him from moving the rest. Their choice of Tan So was a mistake for they realized later that its isolation ..."

References

Military history of Vietnam Military installations of Vietnam {{Vietnam-stub