On 16 February General Louis Brière de l'Isle, the commander of the Tonkin Expeditionary Corps, left Lạng Sơn with Giovanninelli's 1st Brigade to relieve the Siege of Tuyên Quang.

Before his departure, he ordered General Oscar de Négrier, who would remain at Lạng Sơn with the 2nd Brigade, to press on towards the Chinese border and expel the battered remnants of the Guangxi Army from Tonkinese soil.

The Chinese could also rely on the Đồng Đăng stream, a fast-flowing arroyo which ran across the entire front of their line, to act as a moat for their defences and slow down any French attack.

[5] At 9:30 am the French vanguard entered the village of Tham Lon and discovered some unoccupied Chinese forts above the nearby hamlet of Ban Vinh.

Tonnot deployed a section of de Saxcé's battery to give covering fire if necessary, but the Chinese fell back and occupied a rise at a right angle to the road.

One kilometre (0.62 mi) to the north of Ban Vinh there was a tall hill which looked as though it would offer a good view of the Đồng Đăng valley, where the Chinese were presumably entrenched.

De Négrier sent a galloper back to the column's main body with orders for Roperh to deploy his battery on the summit of the hill, now christened by the French 'Bérard Mound'.

But this deployment, in hilly terrain, was a necessarily slow business, and at around midday the Chinese attempted to envelop both French flanks, perhaps hoping to catch them unprepared.

They had more than 2 kilometres (1.2 mi) to march, and before they had covered half this distance they came under fire from a section of French artillery and the three Legion companies deployed to the left of the Mandarin Road.

The Chinese infantry were in considerable strength, and on this occasion were adequately supported by their artillery, which began to engage Roperh's battery from its positions on the cliffs behind Đồng Đăng.

Bérard was shot in the chest and seriously wounded during this counterattack, but Lieutenant de Féraudy immediately assumed command of his company and drove home the French charge.

So far the French infantry on the right of de Négrier's line had shown no signs of advancing, and the Chinese defenders saw no reason to hold their ground under artillery fire.

Most of the houses in the southern part of the town had been set alight by the French artillery bombardment, and the position was now held only by small groups of Chinese skirmishers.

The French conscripts moved forward at a brisk trot and eventually reached the Đồng Đăng stream, 200 metres (660 ft) from the outskirts of the town.

Once they clambered onto dry land the soldiers had only one thought: to reach the shelter of Đồng Đăng and escape from the plunging fire from the limestone massif.

In complete disorder, running at full tilt to close the distance as quickly as possible, the young soldiers of the 111th Battalion charged wildly into the blazing town.

The astonished company officers raced to place themselves at the front of this impromptu charge, waving their swords above their heads to spur on their men to yet greater efforts.

The 111th Battalion and the two supporting Legion companies had already reached the summit at its southern tip and now moved along its eastern edge, clearing the enemy from their vantage points above the Mandarin Road.

[11] It only remained to deal with a strong enemy force holding a hill just to the northeast of Đồng Đăng, which overlooked the entrance to the valley leading to the Chinese frontier and prevented the French from advancing up the Mandarin Road.

The gate itself was protected by two flanking forts and trenches had also been dug along the slopes of the neighbouring hills, but the Chinese troops occupying these defences had been brought forward during the battle to join their comrades around Đồng Đăng.

Lascombes and de Féraudy's companies, on the hills to the east of the Mandarin Road, made their way down into the Đồng Đăng valley and reached the Gate of China shortly after Schoeffer's men.

A sizeable contingent of fresh troops under the command of Feng Zicai (馮子才) was left to cover a border crossing several kilometres to the east of Đồng Đăng, and took no part in the battle.

The news that the French were on Chinese soil caused panic in Longzhou (Lung-chou, 龍州) and other provincial towns close to the Vietnamese border.

De Négrier erected a wooden placard on the ruins of the Gate of China, inscribed in Chinese with the words 'It is not stone walls that protect frontiers, but the faithful execution of treaties'.

The message was a pointed allusion to the Bắc Lệ ambush in June 1884, in French eyes a treacherous violation by the Chinese of the terms of the Tientsin Accord, signed between France and China on 11 May 1884.

[16] Three weeks later the Chinese attacked the Đồng Đăng garrison, precipitating a series of events that led to the French defeat at the Battle of Bang Bo (24 March 1885).