Olivier de Puymanel

The Citadel of Saigon was built by Olivier de Puymanel according to the designs of Théodore Lebrun, following the principles of Vauban, in 1790. Victor Olivier de Puymanel (1768 in Carpentras – 1799 in Malacca), Nguyễn Văn Tín (阮文信) or Ông Tín in Vietnamese, was a French construction officer and a French Navy volunteer and adventurer who had an important role in Vietnam in the 18th century. He played a key role in the modernization of the army of Nguyễn Phúc Ánh (the future Emperor Gia Long).

Olivier de Puymanel was second-class volunteer on board the French warship Dryade. In 1788 he deserted his ship while in Pulo Condor. He soon entered into the service of the Vietnamese prince Nguyễn Phúc Ánh at the instigation of Pigneau de Behaine, who was setting up a force of French volunteers to help the latter regain the throne.

Olivier de Puymanel supervised the construction of the Citadel of Saigon,

He also trained Vietnamese troops in the modern use of artillery, and implemented European infantry methods in the Vietnamese army of Nguyễn Phúc Ánh.

Puymanel is said to have help organize train the men of Nguyen's army, while Dayot was in charge of the Navy. The results of these French efforts at the modernization of Vietnamese forces were attested by John Crawfurd, who visited Huế in 1822:

Olivier de Puymanel also worked on the cartography of the Vietnamese coast, together with Jean-Marie Dayot, another French officer in the service of Nguyễn Phúc Ánh.

Pigneau de Behaine and Puymanel seem to have disliked each other, and Pigneau was rather unimpressed with Puymanel's drinking habits and reliance on Saigon prostitutes.