The Battle of Wagram commences on this day in 1809, considered the largest battle of the Napoleonic Wars.
In 1809, the French military presence in Germany was diminished as Emperor Napoleon I transferred a number of soldiers to fight in the Peninsular War. As a result, the Austrian Empire saw its chance to recover some of its former sphere of influence and invaded the Kingdom of Bavaria, a French ally. Recovering from his initial surprise, Napoleon beat the Austrian forces and occupied Vienna at the beginning of May 1809. Despite the string of sharp defeats and the loss of the empire’s capital, the commander of the Austrian forces Archduke Charles of Austria-Teschen salvaged an army, with which he retreated north of the Danube. This allowed the Austrians to continue the war but, towards the end of May, Napoleon resumed the offensive, suffering a defeat at the Battle of Aspern-Essling.
It took Napoleon six weeks to prepare his next offensive, for which he amassed a 165,000-man French, German and Italian army in the vicinity of Vienna. The Battle of Wagram began after Napoleon crossed the Danube with the bulk of these forces during the night of 4 July and attacked the 145,000-man strong Austrian army. Having successfully crossed the river, Napoleon attempted an early breakthrough and launched a series of evening attacks against the Austrian army. The Austrians were thinly spread in a wide semicircle, but held a naturally strong position. After the attackers enjoyed some initial success, the defenders regained the upper hand and the attacks failed ending the first day of the battle.