Dong Dang Fortress is located to the south of Dong Dang Town, 2km southwest of Huu Nghi (Youyi Quan) Border Gate between Vietnam and China.
The fortress is on a hill with good views of Route 1A between Dong Dang and Lang Son City, route 1B between Lang Son and Thai Nguyen Province, Route 4A between Lang Son and Cao Bang. Dong Dang Fortress has a militarily strategic position.
Dong Dang Fortress was built by the French in 1940 with three storeys measuring 60mx100m: the highest level for observation, second level for gun holes, lowest level for function rooms and weapon storage.
Dong Dang fortress was impregnable in the period 1940-1944. The Viet Minh took the fortress briefly when the Japanese took a coup d'etat against the French in 1945. The French retook the fortress in 1946. In 1950, the French lost during the Viet Minh's Border Campagin in 1950 and tried to blow up Dong Dang Fortress which did only minor damage to the structure.
In the early morning of 17-February-1979, the Chinese fired a few barrages of artillery into Dong Dang as usual. But more and more barrages were followed which was unusual. It was preparation for Chinese infantry invasion of Vietnam... Hundreds of civilians in Dong Dang fled for shelters and many came to Dong Dang Fortress naturally. At the time, the fortress had been protected by a company of border police (over a 100 fighters) half of which was dispatched back to the rear line for unknown reason right before the battle started. The remaining 50 fighters of the border police force was coordinated by a company of the 3rd Division ( of the Military Zone No. 5).
The Chinese overtook various high points in Dong Dang Town and fierce battles took place on the high points around Dong Dang Fortress. From the fortress and the cliffs on the mountains, defensive attacks on the invaders were persistent... But the defenders were running out of food, ammunition and drinking water.
After five days of besiege, the Chinese invaders decided to destroy the whole fortress using 10 tons of dynamite on 22-February-1979. Only about 6 of the defenders found way out and escaped, the rest were killed inside the fortress and in the tunnels. The four entrances and tunnels were mostly destroyed, only those from the east and west had some part of the tunnels not damaged.
At 20:00 hours of 22-February-1979, Dong Dang Fortress and a group of co-ordinated highpoints around the position were overrun. On 23-February-1979, the whole town of Dong Dang was overrun by the Chinese invaders.
