They were selecting the sites for the series of pontoon bridges that were to be thrown across the final stretch of the Danube. The first attempt to cross at the end of May had ended in a humiliating reverse that had cost thousands of lives, including that of Marshal Lannes. Napoleon’s enemies across Europe had been greatly encouraged by the news from Austria. The only way to retrieve the situation was to deliver a crushing blow against Archduke Charles and his army.

The difficulty was that the Danube separated Napoleon from his prey. In addition, the Austrian army had erected a formidable array of field fortifications in a wide arc that stretched across most of the bank that faced Lobau. The enemy had made no moves to carry the fight to Napoleon and seemed content to sit and wait for him.

With all Europe watching the conflict, Napoleon was determined to make another attempt to cross the river, and this time the result would be very different.

Every soldier that could be spared had been summoned to Vienna, where the army steadily increased in size until over a hundred and sixty thousand men had gathered to take part in the attack on Archduke Charles. The troops left to guard the army’s communications with France were thinly stretched and if only one more of the European powers chose to intervene on the side of Austria then there would be little to stand in their way.

Meanwhile Lobau was turned into a fortress. By the end of June over a hundred and thirty cannon were sited in batteries covering the far bank. Two strong bridges had been constructed across the main channel of the Danube as well as three new pontoon bridges. Stakes had been driven into the river bed upstream of the bridges to ensure that they would be protected from any Austrian fireships or floating rams. There was to be no dependence on a single, vulnerable bridge across the river this time.

The enemy had made no attempt to intervene. The French had even managed to land a force across the river to seize the salient on which the hamlet of Mühlau stood. Within hours the French engineers had thoroughly fortified the village and mounted powerful batteries in redoubts to cover the approaches. The enemy had reacted with their usual plodding deliberation and by the time a column had arrived to retake the village it was clear to Archduke Charles that it would cost him far more men than the village was worth and he opted to enclose the salient within the wider system of fieldworks designed to contain any French attempt to break out on to the Marchfeld. Napoleon had been careful to ensure that the Austrians saw the construction of the elaborate series of batteries to cover a landing between Aspern and Essling. Moreover, the elite Imperial Guard had loudly paraded opposite Mühlau, and two additional bridges had been constructed to the salient. The enemy could hardly be in any doubt where Napoleon’s blow would fall.