On 13 May Napoleon entered Vienna, the Austrian capital, after feeble resistance. Since all bridges across the Danube were destroyed, Napoleon now decided on a crossing downstream via Lobau island before Austrian reinforcements could arrive. The pontoon bridge to Lobau island was constructed and crossed on 20 May by troops of Molitor’s Division and Massena’s Corps who deployed across a smaller bridge to the far bank occupying with little resistance the area between the villages of Aspern and Essling. Around 20,000 French troops had reached the far bank when the first breach of the main pontoon bridge occurred; the Austrians floated heavy logs and barges into the fast-flowing current of the Danube, interrupting the flow of French troops to the battle. French forward positions and Massena’s IV Corps became heavily engaged with advancing Austrian formations until night fell (Phase 1). After repairs were made to the bridge, French reinforcements crossed during the night of 21/22 May. French forces, now numbering some 50,000, faced 100,000 Austrian who were closing on the bridgehead. A grim struggle was now fought along the front, Napoleon ordered a renewed attack on the Austrian centre, supported by Lannes’ II Corps. Seeing the Austrian centre falling back, Archduke Charles led his cavalry reserve and succeeded in halting the French advance then driving them back. At this crucial moment the main pontoon bridge was damaged again. Realising his precarious position, Napoleon halted the attack finally ordering his army to withdraw to Lobau island, leaving the Austrians in possession of the battlefield (Phase 2). The attempt to cross the Danube had cost the French 22,000 casualties, including Marshal Lannes, one of Napoleon’s most talented commanders. Meanwhile the Austrian losses numbered 20,000. The battle was Napoleon’s first major defeat.
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