As he watched the attack on the fort he had visited shortly before he saw the remains of the column that had been savaged by the canister fire struggling to get in through the embrasures. The ditch was littered with bodies and those who had reached the rampart were not carrying any ladders and were having to clamber up on to the shoulders of their comrades. Another column was sweeping round the left flank of the fort, hoping to make the most of the distraction caused by their comrades. A ripple of flames from the French guns on the far side of the Elbe announced their entry into the battle and roundshot ploughed through the column.

The assault reached a climax shortly after noon as the Austrians brought their guns closer to the city and attempted to blast gaps in the defences guarding the suburbs. The men in the forts took full advantage of the opportunity to lay down a devastating fire on the enemy batteries, blasting gun crews to ribbons, and smashing their gun carriages. The enemy endured an hour of the cruel punishment before withdrawing the cannon and continuing the assault with infantry. But without any scaling equipment all their discipline and courage came to nothing as they stalled in front of the French lines. St-Cyr’s men held on grimly through the afternoon and as the cathedral clock struck five Napoleon decided that it was time to launch his counter-stroke.

Climbing down from the tower he emerged into the nave and summoned Berthier. ‘The Imperial Guard’s hour has come. Tell Murat and Ney to drive the enemy back. But they are not to lose their heads. The Guard is to advance no more than a mile from the outer works, and then fall back. Be sure that they understand that.’

‘Yes, sire. And what of Mortier? Is he to be held in reserve?’

‘What, and risk the wrath of his guardsmen?’ Napoleon chuckled. ‘I think I had better deal with them myself and put an end to their grumbling.’

‘Be careful, sire,’ Berthier said, in parting, as Napoleon hurried out of the cathedral to mount his horse. He rode east through the streets whose walls echoed the roar of the cannonade and shook under the reverberation of the artillery of both sides. Mortier was waiting at the head of his men, formed up in the confines of a large market square close to the edge of the eastern suburbs. The men, many sporting fine bushy moustaches and the gold earrings that had become something of a fashion amongst the elite corps, were called to attention as their Emperor came in sight. Napoleon slowed his horse to a walk as he made his way down the front rank, scrutinising the silent faces as they stared straight ahead, muskets held at the slope, the tall bearskins making them look like giants.