The battle, fought on 23 and 24 March 1885 on the Tonkin-Guangxi border, saw the defeat of 1,500 soldiers of General François de Négrier's 2nd Brigade of the Tonkin Expeditionary Corps by a Chinese army under the command of the Guangxi military commissioner Pan Dingxin (潘鼎新).

[9] The battle set the scene for the French retreat from Lạng Sơn on 28 March and the conclusion of the Sino-French War in early April in circumstances of considerable embarrassment for France.

On 17 February 1885 General Louis Brière de l'Isle, the general-in-chief of the Tonkin Expeditionary Corps, left Lạng Sơn with Lieutenant-Colonel Laurent Giovanninelli's 1st Brigade to relieve the Siege of Tuyên Quang.

After resupplying the 2nd Brigade with food and ammunition, de Négrier defeated the Guangxi Army at the Battle of Đồng Đăng on 23 February and cleared it from Tonkinese territory.

For good measure, the French crossed briefly into Guangxi province and blew up the 'Gate of China', an elaborate Chinese customs building on the Tonkin-Guangxi border.

By early March, in the wake of the French victories at Hòa Mộc and Dong Dang, the military situation in Tonkin had reached a temporary stalemate.

Substantial French reinforcements reached Tonkin in the middle of March, giving Brière de l'Isle a brief opportunity to break the stalemate.

[8] By the middle of March nine separate Chinese military commands were massed close up to the Tonkinese border around the enormous entrenched camps of Yen Cua Ai and Bang Bo.

Two to three kilometres (1.2 to 1.9 mi) behind Yen Cua Ai, around the village of Mufu, lay the commands of Su Yuanchun and Chen Jia (陳嘉), perhaps 7,000 men in all.

Fifteen kilometres (9.3 mi) behind Mufu the commands of Jiang Zonghan (蔣宗汉) and Fang Yusheng (方友升), also 7,000 strong, were deployed around the village of Pingxiang (known to the French from its Vietnamese pronunciation as Binh Thuong).

Finally, 15 kilometres (9.3 mi) to the east of Zhennanguan, just inside Tonkin, Wang Debang occupied the village of Cua Ai with 3,500 men.

On 22 March, Chinese forces under the command of Feng Zicai（冯子材）raided the French forward post at Dong Dang, a few kilometres north of Lạng Sơn.

This engagement, known as the Battle of Zhennan Pass in China, is normally called Bang Bo in European sources, after the name of a village in the centre of the Chinese position where the fighting was fiercest.

The French took a number of outworks on 23 March, and defeated a hesitant Chinese counterattack against their right flank launched by Wang Debang from Cua Ai.

Herbinger, who was instructed to guide Diguet and Farret to their attack positions, led the two battalions in a wide outflanking march in thick fog, and lost his way.

Two of the four companies of the 111th Battalion reached the trench, but after a short spell of hand-to-hand fighting were thrown back by a Chinese counterattack led personally by Feng Zicai.

A collection of his letters from Tonkin, including a number of vivid descriptions of the February campaign to capture Lạng Sơn, would be published posthumously in France in 1886.

Meanwhile, Schoeffer's 3rd Legion Battalion, which had been ordered to remain on Tonkinese soil around Dong Dang to protect the flanks of the French column, fought desperately to keep open a line of retreat for the 2nd Brigade.

Schoeffer's men beat off strong Chinese attacks on both French flanks, enabling the other three infantry battalions and the two artillery batteries to make good their retreat.

On 28 March de Négrier was seriously wounded in the battle of Kỳ Lừa,[18] in which the Tonkin Expeditionary Corps defeated an attack by the Guangxi Army on the defences of main base.

The battle of Bang Bo therefore paved the way for the Retreat from Lạng Sơn and the collapse of Jules Ferry's administration on 30 March in the Tonkin Affair.