‘Sweet Jesus!’ he shouted, eyes wide with fear.‘The enemy are on us!’ He turned quickly to one of his men, no more than a youth, holding the smouldering taper. ‘Light the fuse! Do it now!’

Then he turned and scrambled up the bank, brushing past Napoleon as he ran along the causeway. Another shot struck the surface of the river close to the young engineer and he ducked and lit the end of the fuse.

‘No! Don’t!’ Napoleon shouted, thrusting out his hands.

There was a bright flare, and then the spark raced along the fuse, hissing and spitting like a demon as it followed the loops of cord towards the central arches of the bridge. One of the guardsmen escorting Napoleon grabbed his sleeve and hauled him away.

‘Take cover, sire!’

They stumbled across the bank of the river, making for the shelter of a low stone wall. The guardsman heaved Napoleon over the wall and dived after him, just as there was a blinding flash that shot jets of flame and smoke into the air. The concussion hit them with a deafening roar. Napoleon glanced up and saw chunks of masonry, men and limbs blasted into the air, where they hung for an instant before tumbling back down. A slab of paving smashed through the tiled roof of the house adjoining the wall.

For a moment Napoleon sat on his hands and knees, stunned by the ferocity of the blast. Then he scrambled up and looked over the wall. The central arches of the bridge had gone and the water beneath was churning as the lighter bits of debris rained down. A gap nearly a hundred feet wide had been blown out of the bridge and on either end the stonework was scorched black. Further back the bodies of his men lay heaped on the cobbles of the roadway. Here and there a dazed survivor struggled to free himself from the bloody carnage. On the far bank a crowd of men stood and stared, aghast. Their only escape route from Leipzig was gone. A collective groan reached Napoleon’s ears from across the river.

‘Oh, shit,’ the guardsman muttered. ‘They’re fucked.’

Napoleon nodded. Already he could hear the sounds of musketry increasing in intensity as the enemy pressed forward against the French rearguard. Some of the men on the far bank looked round anxiously and then the first of them threw down his musket and struggled out of his backpack. Stripped down to shirt, breeches and boots, he clambered down into the current and struck out for the opposite bank. More followed suit, some clinging to small kegs and other items that would give them buoyancy. Most made it across, heaving themselves up on to the grassy bank either side of Napoleon. Some, poor swimmers or injured, were carried away by the current, and thrashed for a moment before being dragged beneath the surface by the weight of their uniforms and equipment.