The Germans were now on the alert to entrap this army that exposed its flank in a long line of march near to the Belgian frontier. Their ubiquitous horsemen captured French despatches which showed them the intended moves in MacMahon's desperate game; Moltke hurried up every available division; and the elder of the two Alvenslebens had the honour of surprising de Failly's corps amidst the woods of the Ardennes near Beaumont, as they were in the midst of a meal. The French rallied and offered a brisk defence, but finally fell back in confusion northwards on Mouzon, with the loss of 2000 prisoners and 42 guns (August 30).
This mishap, the lack of provisions, and the fatigue and demoralisation of his troops, caused MacMahon on the 31st to fall back on Sedan, a little town in the valley of the Meuse. It is surrounded by ramparts planned by the great Vauban, but, being commanded by wooded heights, it no longer has the importance that it possessed before the age of long-range guns of precision. The chief strength of the position for defence lay in the deep loop of the river below the town, the dense Garenne Wood to the north-east, and the hollow formed by the Givonne brook on the east, with the important village of Bazeilles. It is therefore not surprising that von Moltke, on seeing the French forces concentrating in this hollow, remarked to von Blumenthal, Chief of the Staff: "Now we have them in a trap; to-morrow we must cross over the Meuse early in the morning."
The Emperor and MacMahon seem even then, on the afternoon of the 31st, to have hoped to give their weary troops a brief rest, supply them with provisions and stores from the fortress, and on the morrow, or the 2nd, make their escape by way of Mézières. Possibly they might have done so on that night, and certainly they could have reached the Belgian frontier, only some six miles distant, and there laid down their arms to the Belgian troops whom the resourceful Bismarck had set on the _qui vive._ To remain quiet even for a day in Sedan was to court disaster; yet passivity characterised the French headquarters and the whole army on that afternoon and evening. True, MacMahon gave orders for the bridge over the Meuse at Donchéry to be blown up, but the engine-driver who took the engineers charged with this important task, lost his nerve when German shells whizzed about his engine, and drove off before the powder and tools could be deposited. A second party, sent later on, found that bridge in the possession of the enemy. On the east side, above Sedan, the Bavarians seized the railway bridge south of Bazeilles, driving off the French who sought to blow it up[44].