He was interrupted by a faint roar and looked towards Vienna. Beyond the city skyline he could see a billowing column of smoke rising up into the clear sky. A moment later there was a second explosion and more smoke, followed by two more blasts that echoed across the landscape towards the startled leading elements of the French army.

‘They’ve blown the bridges,’ Berthier said quietly.

Napoleon nodded, and glared at Baron Karinsky. ‘Tell the mayor Vienna is to surrender unconditionally. If he does not surrender the city within the hour, then I will order my guns to pulverise your capital. Is that clear?’

Karinsky shook his head. ‘Sire, I am not authorised to negotiate with you. My master simply sent me here to invite you to speak with him.’

‘There is nothing to say. There will be no negotiations. Tell him that I demand he surrender, and that if he fails to do so then the death and destruction that I will rain down on Vienna will be his responsibility.’

The Austrian opened his mouth to protest but Napoleon took out his watch and glanced down briefly. ‘It is now just gone eleven o’clock. If the city has not surrendered by noon I will order the guns to open fire. It would be wise of you to waste no time in informing the mayor of my terms.’

Karinsky frowned and then abruptly turned his horse about and spurred it into a gallop as he headed back down the road to Vienna.

As soon as the gates of Vienna were thrown open to the French army, Napoleon and his chief engineer, General Bertrand, rode through the city to assess the condition of the demolished bridges. The Austrian engineers had done a thorough job. The central spans of each bridge had been blown, and the buttressed piles were little more than heaps of masonry in the swiftly flowing current of the Danube. On the far side of the river the enemy was busy building barricades across the ends of the ruined bridges. On the flanks artillery batteries were being constructed to cover the river in case the French engineers attempted to make any repairs to the blown spans.

Napoleon gazed at the bridges with a heavy heart. The enemy would be safe until the French could find another way across the river.

General Bertrand had finished surveying the bridges and the Austrian forces beyond, and clicked his tongue. ‘It would be suicide to attempt any repairs, sire.’

‘I can see that for myself,’ Napoleon replied testily. ‘If we can’t cross here, then we must find somewhere else.’