The battle was fought to clear Chinese forces away from the French forward base at Chu, and was an essential preliminary to the Lạng Sơn Campaign in February 1885.

[5] In late September 1884, large detachments of the Guangxi Army advanced from Lạng Sơn and probed into the Luc Nam valley, announcing their presence by ambushing the French river gunboats Hache and Massue (of the Tonkin Flotilla) on 2 October.

[citation needed] In the wake of these French victories, the Chinese fell back to Bắc Lệ and Dong Song, and de Négrier established important forward positions at Kép and Chu, which threatened the Guangxi Army's base at Lạng Sơn.

De Négrier immediately brought up reinforcements and pursued the Chinese, but the raiders made good their retreat to Dong Song.

A week after this engagement a force of 12,000 Chinese troops from the Guangxi Army occupied the distinctive conical hill of Núi Bop, 18 kilometres (11 mi) to the east of Chu, and began to lay out a large fortified camp.

The Chinese force was under the command of Wang Debang, one of the Guangxi Army's more competent generals, who had defeated a French column in June 1884 in the Bắc Lệ ambush.

On 23 December the villagers of Lien Son came to the French headquarters at Chu and alerted Lieutenant-Colonel Donnier to the presence of a large Chinese force around Núi Bop.

[8] The French could not allow a force of 12,000 Chinese to remain at Núi Bop, uncomfortably close to their main base at Chu and threatening the flank of the expeditionary corps when it eventually set off for Lạng Sơn.

To divert the enemy's attention while his main column marched around the Chinese, chef de bataillon Diguet's Legion battalion in Chu would demonstrate against their front.

The French had been told that the ford could be crossed easily, but they discovered that the northern bank of the Luc Nam river was more than nine feet high at Dao Be and almost sheer.

The French column had been spotted fording the river, and the delay in completing the crossing had given the Chinese just enough time to prepare to meet its attack.

The French artillery took a position on a hill to the right of the path and opened fire on the Chinese skirmishers, while de Négrier gave his orders for the attack.

The marine infantry were ordered to attack the wood frontally, while the 143rd Battalion was to climb the hills to the right to flank the enemy's position and push back the Chinese left wing into the Phong Cot valley.

[15] The Chinese soldiers facing de Négrier's men in this part of the field wore a distinctive covering of tawny material with black stripes on their heads and shoulders.

[15] The leading French units pressed on and cleared the Chinese from the hills around Phong Cot, while the rest of de Négrier's column continued its crossing of the Luc Nam.

While his company tried to defend itself with close-range rifle fire Verdier ordered one of his men to try to make his way through the Chinese lines back to Phong Cot and ask for help.

A young private soldier named Meffret crept cautiously through the Chinese lines in the fading gloom of night and reached Phong Cot, where he delivered Verdier's message to Lieutenant-Colonel Herbinger.

[18] Herbinger, perhaps believing that Meffret was exaggerating the danger, responded by sending forward from Phong Cot a single section of the 111th Battalion—a mere ten men.

The main Chinese defence line consisted of a trench between Phong Cot and the Siou Nien River, which protected the road that ran from Lien Son to Cao Say.

The French took possession of two abandoned Krupp artillery batteries and large quantities of rifles, clothes, tents and food.

The French scoured the battlefield during the afternoon of 4 January, and killed all the wounded Chinese soldiers they could find with pistol shots to the head.

[24] A number of unwounded Chinese soldiers were taken prisoner by the French at Núi Bop and subsequently interrogated for their knowledge of the Guangxi Army's order of battle.

[25] On 5 January 1885 General Brière de l'Isle issued the following order of the day to commemorate the victory at Núi Bop: Deux brillants succès pour le corps expéditionnaire ouvrent l'année 1885.

Repoussés, poursuivis et enfin rejetés sur Nui-Bop, ils étaient en pleine déroute avant midi.

On 3 January, after a march skillfully concealed from the enemy's eyes, General de Négrier fell upon a cantonment of 6,000 regulars at 4 pm and would have completely routed them, despite their lively resistance, in less than two hours had not nightfall prevented him from pursuing his initial success.

Nui Bop, the centre of their resistance, defended by eight solidly organized forts, is in our hands, with two Krupp batteries and all the enemy's material: tents, food, ammunition, weapons and standards.

De Nègrier's victory at Núi Bop, won at odds of just under one to ten, was regarded by his fellow-officers as the most spectacular professional triumph of his career.