Tân Sở citadel was a secret military base in central Vietnam that was built in the 1880s. It was built up by Tôn Thất Thuyết, the regent of the

Nguyễn dynasty The Nguyễn dynasty (chữ Nôm: 茹阮, vi, Nhà Nguyễn; chữ Hán: 阮朝, vi, Nguyễn triều) was the last Vietnamese dynasty, which ruled the unified Vietnamese state largely independently from 1802 to 1883. During its existence, ...

, 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