On February 17, 1859, the Franco-Spanish forces under Vice Admiral Rigault de Genouilly attacked and captured Gia Dinh Citadel after a prolonged battle. The Nguyen dynasty forces commanded by Vu Trong Binh could not withstand the overwhelming firepower of the invaders and were forced to retreat.
The background to this attack was France's colonial expansion policy in Asia during the 19th century. After failing to make headway at Da Nang in 1858, Genouilly decided to redirect his forces southward, where river access was more favorable and defenses were weaker. Gia Dinh occupied a strategic position on the Saigon River — the gateway to the rice-rich Mekong Delta.
Gia Dinh Citadel at the time was a Vauban-style defensive fortification (French military architecture), built during the reign of Nguyen Anh. Nevertheless, with a fleet of steamships, long-range cannon, and superior numbers, the Franco-Spanish forces demolished the fortifications within a few hours of fighting. Immediately after taking the citadel, French forces tore down the walls and began redesigning the city along European urban lines.
The fall of Gia Dinh Citadel in 1859 was a tragic turning point in the history of Saigon — Gia Dinh. It marked the beginning of nearly a century of French colonial rule, leading to Cochinchina becoming a French colony in 1862, with Central and Northern Vietnam following. It was during this period that the French redesigned Saigon into the 'Pearl of the Far East' — with its grand boulevards and Neo-Classical architecture that still stand today.
The resistance movement of the Southern Vietnamese people erupted immediately. Leaders such as Truong Dinh (1820–1864) refused to stand down despite the royal court signing the Treaty of Saigon in 1862. Nguyen Trung Truc (1838–1868) is remembered for his defiant words: 'Only when the Westerners have uprooted all the grass of Vietnam will there be no more Vietnamese fighting them.' This spirit of resistance became the inspiration for the patriotic movement over the next 80 years.