As soon as the guns were in place, Bessiиres withdrew his battered cavalry divisions and there was another brief lull as the enemy squares formed back into lines and then advanced, en masse, towards the waiting Italians of Prince Eugиne, and the hurriedly assembled battery defending the centre of the Grand Army. With a thunderous roar the guns tore into the enemy lines, carving bloody paths through the leading ranks. Napoleon could only wonder at their discipline as the Austrians closed up the gaps and continued at a steady pace, muskets sloped.

‘My God, Berthier, those men are fearless.’

Berthier nodded, eyes fixed on the terrible carnage being wrought by the continuous blasts of the French guns. Over a thousand men must have been cut down before they came within musket range of the French line. Still their discipline held as their officers gave the order to shoulder their weapons and take aim on the French. Their first volley whirred through the dense smoke hanging in front of the cannon, striking down scores of the gunners. A second volley did as much damage, and there was a brief pause before the first company of Imperial Guardsmen were ordered forward to serve the guns. They slung their muskets over their shoulders and did as they were bid by the artillerymen who had survived the initial volleys.

The two lines stood their ground, the French guns and muskets of Eugиne’s men answered by the massed volleys of the Austrians. Napoleon watched the mutual slaughter without expression. Thousands had fallen, and all the time more were struck down, falling upon the heaped bodies of their comrades. It was a small mercy that the smoke became so thick that it hid the true scale of the horror from the men locked into a mechanical ritual of firing and reloading as swiftly as they could. The carnage amongst the gun crews in front of Napoleon’s position numbed his staff officers, who sat in their saddles and watched the bloody spectacle in silence.

For nearly an hour the firing continued. In that time Napoleon had news that Massйna had managed to form his men up in front of Essling and was starting to push the Austrians back. The cannon on Lobau island were firing across the river into the enemy’s flank, and under attack on three sides they could only endure so much before falling back. On the other side of the battlefield Marshal Davout was also steadily pushing the enemy back. Napoleon glanced at his watch and saw that it was almost noon. He turned to Berthier.

‘It seems that the enemy’s attacks have been checked, and the last of their reserves are committed to the battle. Now is the time for us to mount our own assault, break the Austrian line and defeat the army of Archduke Charles.’

The Emperor’s chief of staff looked round the battlefield. ‘Sire, we have few enough reserves of our own. Would an attack be prudent?’

‘Prudent?’ Napoleon shook his head in pity. ‘Have you no faith in me, Berthier?’

Berthier lowered his gaze.

Napoleon continued. ‘Send orders for the army to attack along the entire line. The main blow will be delivered there.’ He raised his hand and pointed to the ground west of Aderklaa.

‘Yes, sire. And who is to have that task?’

Napoleon thought a moment.‘General MacDonald. His men are the freshest troops we have on the field.’

‘They are also some of the most inexperienced,’ Berthier countered.

‘Even so, they will win the battle for me. What greater glory could a new soldier ask for? Tell MacDonald to form his men up to attack.’

Hundreds of cannon rumbled along a battle line that stretched from the Danube to Wagram, and then down the line of the Russbach river, a distance of nearly eight miles. Opposite the Austrian centre, General MacDonald led his men forward. Eight thousand of them, their battalions arranged in a huge square formation. As soon as the drums beat the advance, the formation marched forward. The men were sweating freely in their stifling uniforms. The ground before them was a patchwork of trampled fields, strewn with bodies and abandoned equipment from two days of fighting. The dead had begun to corrupt in the midsummer heat and the air was thick with the stench of decaying flesh, blood and shit. Clouds of flies and other insects created a steady drone as they gorged themselves.

Ahead, the leading ranks could see the enemy artillery crews hurriedly repositioning their guns as they spied the new threat through the thinning clouds of gunpowder smoke.

‘MacDonald’s men will make a fine target, sire,’ said Berthier. ‘That square of his will be impossible to miss.’

Napoleon did not respond, but just continued to watch intently as the first of the Austrian batteries opened fire. The range was long, and they had loaded the guns with roundshot. The heavy iron balls grounded with a puff of dry soil a short distance in front of the leading battalion before ricocheting through the ranks, mowing down every soldier in their path. More guns opened up and MacDonald’s division began to lose scores of men with each minute that passed. Their progress across the plain was marked by a bloody trail of dead and wounded. As they came within range of case shot the nearest guns unleashed a devastating hail that wreaked even more slaughter on the diminishing French ranks.

Berthier shook his head in wonder. ‘My God, they can’t take much more of this.’

Napoleon sucked in a breath through his teeth. ‘Pray that they do.’

The square staggered on, coming in range of the Austrian skirmishers, who added their fire to the cannon. MacDonald had already lost half his men, Napoleon estimated, yet still they advanced into the teeth of the enemy’s cannon and muskets. At last the survivors were close enough to the enemy line to fire their first volley in reply. The leading battalions deployed, loaded and raised their muskets, and fired at the nearest enemy guns and infantry formations. Napoleon felt a moment of blissful vengeance as the distant figures of Austrian artillerymen were cut down beside their guns.

MacDonald ordered the square to advance again and it pressed on, pausing to fire another volley before bayonets were fixed and they charged into the line of Austrian infantry waiting beyond.

The terrible tension of waiting for the division to get into action gave way to anxiety that MacDonald’s men had suffered too many casualties to carry the day. Napoleon nodded to himself as he made a decision.‘Berthier, we need every available man to support MacDonald! We must send forward what is left of Eugиne’s reserves, and also the Imperial Guard.’

Berthier raised his eyebrows. ‘But sire, then we will have no reserves left. Nothing to face Archduke John should he reach the field.’

Napoleon gestured towards the two battalions assigned to guard the headquarters. ‘That will be our reserve. Send them to cover our right, and order the rest forward to save MacDonald, before it is too late.’

As the reinforcements swiftly advanced over the torn-up plain, Napoleon read through the latest reports from the other sectors of the battlefield. Davout and Massйna were driving back the Austrian flanks and Wagram had been taken by Prince Eugиne and his men. Satisfied that the battle was tilting in his favour, he turned his attention back to the centre. With the aid of the fresh troops Napoleon had sent him, MacDonald was pushing steadily through the Austrian centre. Both sides were exchanging volleys at point-blank range and bodies lay in heaps across the battlefield. The arrival of the Imperial Guard proved to be decisive. After delivering one volley, they charged the Austrian line. There was a brief and bitter struggle and then the enemy broke, thousands of their men scrambling away towards the shelter of the hills running along the edge of the plain to the north.

At long last the Austrian army had been broken in two.