middle of March, giving Brière de l'Isle a brief opportunity to break the stalemate. He moved the bulk of the reinforcements to Hưng Hóa to reinforce the 1st Brigade, intending to attack the Yunnan Army and drive it back beyond Yen Bay. While he and Giovanninelli drew up plans for a western offensive, he ordered de Négrier to hold his positions at Lang Son. On 23 and 24 March the 2nd Brigade, only 1,500 men strong, fought a fierce action with over 25,000 troops of the Guangxi Army entrenched near Zhennanguan on the Chinese border. The Battle of Bang Bo (named by the French from the Vietnamese pronunciation of Hengpo, a village in the centre of the Chinese position where the fighting was fiercest), is normally known as the Battle of Zhennan Pass in China. The French took a number of outworks on 23 March, but failed to take the main Chinese positions on 24 March and were fiercely counterattacked in their turn. Although the French made a fighting withdrawal and prevented the Chinese from piercing their line, casualties in the 2nd Brigade were relatively heavy (70 dead and 188 wounded) and there were ominous scenes of disorder as the defeated French regrouped after the battle. As the brigade's morale was precarious and ammunition was running short, de Négrier decided to fall back to Lạng Sơn. The coolies abandoned the French and the French also had supply issues. The Chinese also outnumbered the French. The Chinese advanced slowly in pursuit, and on 28 March de Négrier fought a battle at Kỳ Lừa in defence of Lạng Sơn. Rested, recovered and fighting behind breastworks, the French successfully held their positions and inflicted crippling casualties on the Guangxi Army. French casualties at Kỳ Lừa were 7 men killed and 38 wounded. The Chinese left 1,200 corpses on the battlefield, and a further 6,000 Chinese soldiers may have been wounded. The battle of Kỳ Lừa gave a grim foretaste of the horrors of warfare on the Western Front thirty years later. Towards the end of the battle de Négrier was seriously wounded in the chest while scouting the Chinese positions. He was forced to hand over command to his senior regimental commander, Lieutenant-Colonel Paul-Gustave Herbinger. Herbinger was a noted military theoretician who had won a respectable battlefield reputation during the Franco-Prussian War, but was quite out of his depth as a field commander