In the Battle of Aspern-Essling, Napoleon crossed the Danube near Vienna, but the French and their allies were attacked and forced back across the river by the Austrians under Archduke Charles. It was the first time Napoleon had been personally defeated in a major battle, as well as his first battle defeat in 10 years since the Siege of Acre, and his first battle defeat as head of state.

Archduke Charles Louis John Joseph Laurentius of Austria, Duke of Teschen was an Austrian field-marshal, the third son of Emperor Leopold II and his wife, Maria Luisa of Spain. He was also the younger brother of Francis II, Holy Roman Emperor. He was epileptic, but achieved respect both as a commander and as a reformer of the Austrian army. He was considered one of Napoleon's more formidable opponents and one of the greatest generals of the French Revolutionary and Napoleonic Wars.