What was the biggest battle of the Napoleonic wars. It was in 1812 and 250,000 men took part but I don't know the actual name. I would assume it was in Russia as Tchaikovsky wrote the 1812 Overture.
The Battle of the Nations outside Leipzig in 1813 was the biggest of the Napoleonic Wars. It involved 200,000 French and 300,000 Allied troops. Ref. Alistair Horne 'How Far From Austerlitz'.